Maximum sum submatrix - GeeksforGeeks (2024)

Last Updated : 11 Jul, 2022

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Prerequisite: Kadane’s algorithm

Given a 2D array arr[][] of dimension N*M, the task is to find the maximum sum sub-matrix from the matrix arr[][].

Examples:

Input: arr[][] = {{0, -2, -7, 0 }, { 9, 2, -6, 2 }, { -4, 1, -4, 1 }, { -1, 8, 0, -2}}
Output: 15
Explanation: The submatrix {{9, 2}, {-4, 1}, {-1, 8}} has a sum 15, which is the maximum sum possible.

Input: arr[][] = {{1, 2}, {-5, -7}}
Output: 3

Naive Approach: The simplest approach is to generate all possible submatrices from the given matrix and calculate their sum. Finally, print the maximum sum obtained.

Below is the implementation of the above approach:

C++

// C++ program for the above approach

#include <bits/stdc++.h>

using namespace std;

// Function to find maximum sum submatrix

void maxSubmatrixSum(

vector<vector<int> > matrix)

{

// Stores the number of rows

// and columns in the matrix

int r = matrix.size();

int c = matrix[0].size();

// Stores maximum submatrix sum

int maxSubmatrix = 0;

// Take each row as starting row

for (int i = 0; i < r; i++) {

// Take each column as the

// starting column

for (int j = 0; j < c; j++) {

// Take each row as the

// ending row

for (int k = i; k < r; k++) {

// Take each column as

// the ending column

for (int l = j; l < c; l++) {

// Stores the sum of submatrix

// having topleft index(i, j)

// and bottom right index (k, l)

int sumSubmatrix = 0;

// Iterate the submatrix

// row-wise and calculate its sum

for (int m = i; m <= k; m++) {

for (int n = j; n <= l; n++) {

sumSubmatrix += matrix[m][n];

}

}

// Update the maximum sum

maxSubmatrix

= max(maxSubmatrix,

sumSubmatrix);

}

}

}

}

// Print the answer

cout << maxSubmatrix;

}

// Driver Code

int main()

{

vector<vector<int> > matrix = { { 0, -2, -7, 0 },

{ 9, 2, -6, 2 },

{ -4, 1, -4, 1 },

{ -1, 8, 0, -2 } };

maxSubmatrixSum(matrix);

return 0;

}

Java

// Java program for the above approach

import java.util.*;

class GFG

{

// Function to find maximum sum submatrix

static void maxSubmatrixSum(int[][] matrix)

{

// Stores the number of rows

// and columns in the matrix

int r = matrix.length;

int c = matrix[0].length;

// Stores maximum submatrix sum

int maxSubmatrix = 0;

// Take each row as starting row

for (int i = 0; i < r; i++) {

// Take each column as the

// starting column

for (int j = 0; j < c; j++) {

// Take each row as the

// ending row

for (int k = i; k < r; k++) {

// Take each column as

// the ending column

for (int l = j; l < c; l++) {

// Stores the sum of submatrix

// having topleft index(i, j)

// and bottom right index (k, l)

int sumSubmatrix = 0;

// Iterate the submatrix

// row-wise and calculate its sum

for (int m = i; m <= k; m++) {

for (int n = j; n <= l; n++) {

sumSubmatrix += matrix[m][n];

}

}

// Update the maximum sum

maxSubmatrix

= Math.max(maxSubmatrix,

sumSubmatrix);

}

}

}

}

// Print the answer

System.out.println(maxSubmatrix);

}

// Driver Code

public static void main(String[] args)

{

int[][] matrix = { { 0, -2, -7, 0 },

{ 9, 2, -6, 2 },

{ -4, 1, -4, 1 },

{ -1, 8, 0, -2 } };

maxSubmatrixSum(matrix);

}

}

// This code is contributed by susmitakundugoaldanga.

Python3

# Python3 program for the above approach

# Function to find maximum sum submatrix

def maxSubmatrixSum(matrix):

# Stores the number of rows

# and columns in the matrix

r = len(matrix)

c = len(matrix[0])

# Stores maximum submatrix sum

maxSubmatrix = 0

# Take each row as starting row

for i in range(r):

# Take each column as the

# starting column

for j in range(c):

# Take each row as the

# ending row

for k in range(i, r):

# Take each column as

# the ending column

for l in range(j, c):

# Stores the sum of submatrix

# having topleft index(i, j)

# and bottom right index (k, l)

sumSubmatrix = 0

# Iterate the submatrix

# row-wise and calculate its sum

for m in range(i, k + 1):

for n in range(j, l + 1):

sumSubmatrix += matrix[m][n]

# Update the maximum sum

maxSubmatrix= max(maxSubmatrix, sumSubmatrix)

# Print the answer

print (maxSubmatrix)

# Driver Code

if __name__ == '__main__':

matrix = [ [ 0, -2, -7, 0 ],

[ 9, 2, -6, 2 ],

[ -4, 1, -4, 1 ],

[ -1, 8, 0, -2 ] ]

maxSubmatrixSum(matrix)

# This code is contributed by mohit kumar 29.

C#

// C# program to implement

// the above approach

using System;

public class GFG

{

// Function to find maximum sum submatrix

static void maxSubmatrixSum(int[,] matrix)

{

// Stores the number of rows

// and columns in the matrix

int r = matrix.GetLength(0);

int c = matrix.GetLength(1);

// Stores maximum submatrix sum

int maxSubmatrix = 0;

// Take each row as starting row

for (int i = 0; i < r; i++) {

// Take each column as the

// starting column

for (int j = 0; j < c; j++) {

// Take each row as the

// ending row

for (int k = i; k < r; k++) {

// Take each column as

// the ending column

for (int l = j; l < c; l++) {

// Stores the sum of submatrix

// having topleft index(i, j)

// and bottom right index (k, l)

int sumSubmatrix = 0;

// Iterate the submatrix

// row-wise and calculate its sum

for (int m = i; m <= k; m++) {

for (int n = j; n <= l; n++) {

sumSubmatrix += matrix[m, n];

}

}

// Update the maximum sum

maxSubmatrix

= Math.Max(maxSubmatrix,

sumSubmatrix);

}

}

}

}

// Print the answer

Console.WriteLine(maxSubmatrix);

}

// Driver Code

public static void Main(String []args)

{

int[,] matrix = { { 0, -2, -7, 0 },

{ 9, 2, -6, 2 },

{ -4, 1, -4, 1 },

{ -1, 8, 0, -2 } };

maxSubmatrixSum(matrix);

}

}

// This code is contributed by sanjoy_62.

Javascript

<script>

// Javascript program for the above approach

// Function to find maximum sum submatrix

function maxSubmatrixSum(matrix)

{

// Stores the number of rows

// and columns in the matrix

var r = matrix.length;

var c = matrix[0].length;

// Stores maximum submatrix sum

var maxSubmatrix = 0;

// Take each row as starting row

for (i = 0; i < r; i++) {

// Take each column as the

// starting column

for (j = 0; j < c; j++) {

// Take each row as the

// ending row

for (k = i; k < r; k++) {

// Take each column as

// the ending column

for (l = j; l < c; l++) {

// Stores the sum of submatrix

// having topleft index(i, j)

// and bottom right index (k, l)

var sumSubmatrix = 0;

// Iterate the submatrix

// row-wise and calculate its sum

for (m = i; m <= k; m++) {

for (n = j; n <= l; n++) {

sumSubmatrix += matrix[m][n];

}

}

// Update the maximum sum

maxSubmatrix = Math.max(maxSubmatrix,

sumSubmatrix);

}

}

}

}

// Print the answer

document.write(maxSubmatrix);

}

// Driver Code

var matrix = [ [ 0, -2, -7, 0 ],

[ 9, 2, -6, 2 ],

[ -4, 1, -4, 1 ],

[ -1, 8, 0, -2 ] ];

maxSubmatrixSum(matrix);

// This code contributed by umadevi9616

</script>

Output:

15

Time Complexity: O(N6)
Auxiliary Space: O(1)

Efficient Approach using Kadane’s Algorithm: The above approach can be optimized using the following observations:

  • Fix starting and ending column of the required sub-matrix say start and end respectively.
  • Now, iterate each row and add row sum from starting to ending column to sumSubmatrix and insert this in an array. After iterating each row, perform Kadane’s Algorithm on this newly created array. If the sum obtained by applying Kadane’s algorithm is greater than the overall maximum sum, update the overall maximum sum.
  • In the above step, the row sum from starting to ending column can be calculated in constant time by creating an auxiliary matrix of size N*M containing the prefix sum of each row.

Follow the steps below to solve the problem:

  • Initialize a variable, say maxSum as INT_MIN, to store the maximum subarray sum.
  • Create a matrix prefMatrix[N][M] that stores the prefix array sum of every row of the given matrix.
  • Traverse the matrix row-wise using i as the row index and j as the column index and perform the following steps:
    • If the value of i is 0, then set prefMatrix[i][j] = A[i][j].
    • Otherwise, set prefMatrix[i][j] = prefMatrix[i][j – 1] + A[i][j].
  • Now for all possible combinations of starting and ending index of the columns of submatrix over the range [0, M] perform the following steps:
    • Initialize an auxiliary array A[] to stores the maximum sum for each row of the current submatrix.
    • Find the sum from starting to ending column using prefMatrix as follows:
      • If the value of start is positive, then store the required sum S as prefMatrix[i][end] – prefMatrix[i][start – 1].
      • Otherwise, update S as prefMatrix[i][end].
    • Insert S in an array arr[].
    • After iterating all rows in the submatrix, perform Kadane’s algorithm on the array A[] and update the maximum sum maxSum as the maximum of maxSum and value obtained by performing the Kadane’s Algorithm in this step.
  • After completing the above steps, print the value of maxSum as the result.

Below is the implementation of the above approach:

C++

// C++ program for the above approach

#include <bits/stdc++.h>

using namespace std;

// Function to find maximum continuous

// maximum sum in the array

int kadane(vector<int> v)

{

// Stores current and maximum sum

int currSum = 0;

int maxSum = INT_MIN;

// Traverse the array v

for (int i = 0;

i < (int)v.size(); i++) {

// Add the value of the

// current element

currSum += v[i];

// Update the maximum sum

if (currSum > maxSum) {

maxSum = currSum;

}

if (currSum < 0) {

currSum = 0;

}

}

// Return the maximum sum

return maxSum;

}

// Function to find the maximum

// submatrix sum

void maxSubmatrixSum(

vector<vector<int> > A)

{

// Store the rows and columns

// of the matrix

int r = A.size();

int c = A[0].size();

// Create an auxiliary matrix

int** prefix = new int*[r];

// Traverse the matrix, prefix

// and initialize it will all 0s

for (int i = 0; i < r; i++) {

prefix[i] = new int;

for (int j = 0; j < c; j++) {

prefix[i][j] = 0;

}

}

// Calculate prefix sum of all

// rows of matrix A[][] and

// store in matrix prefix[]

for (int i = 0; i < r; i++) {

for (int j = 0; j < c; j++) {

// Update the prefix[][]

if (j == 0)

prefix[i][j] = A[i][j];

else

prefix[i][j] = A[i][j]

+ prefix[i][j - 1];

}

}

// Store the maximum submatrix sum

int maxSum = INT_MIN;

// Iterate for starting column

for (int i = 0; i < c; i++) {

// Iterate for last column

for (int j = i; j < c; j++) {

// To store current array

// elements

vector<int> v;

// Traverse every row

for (int k = 0; k < r; k++) {

// Store the sum of the

// kth row

int el = 0;

// Update the prefix

// sum

if (i == 0)

el = prefix[k][j];

else

el = prefix[k][j]

- prefix[k][i - 1];

// Push it in a vector

v.push_back(el);

}

// Update the maximum

// overall sum

maxSum = max(maxSum, kadane(v));

}

}

// Print the answer

cout << maxSum << "\n";

}

// Driver Code

int main()

{

vector<vector<int> > matrix = { { 0, -2, -7, 0 },

{ 9, 2, -6, 2 },

{ -4, 1, -4, 1 },

{ -1, 8, 0, -2 } };

// Function Call

maxSubmatrixSum(matrix);

return 0;

}

Java

// Java program for the above approach

import java.util.*;

class GFG{

// Function to find maximum continuous

// maximum sum in the array

static int kadane(Vector<Integer> v)

{

// Stores current and maximum sum

int currSum = 0;

int maxSum = Integer.MIN_VALUE;

// Traverse the array v

for (int i = 0;

i < (int)v.size(); i++)

{

// Add the value of the

// current element

currSum += v.get(i);

// Update the maximum sum

if (currSum > maxSum)

{

maxSum = currSum;

}

if (currSum < 0)

{

currSum = 0;

}

}

// Return the maximum sum

return maxSum;

}

// Function to find the maximum

// submatrix sum

static void maxSubmatrixSum(int [][]A)

{

// Store the rows and columns

// of the matrix

int r = A.length;

int c = A[0].length;

// Create an auxiliary matrix

int [][]prefix = new int[r][];

// Traverse the matrix, prefix

// and initialize it will all 0s

for (int i = 0; i < r; i++) {

prefix[i] = new int;

for (int j = 0; j < c; j++) {

prefix[i][j] = 0;

}

}

// Calculate prefix sum of all

// rows of matrix A[][] and

// store in matrix prefix[]

for (int i = 0; i < r; i++) {

for (int j = 0; j < c; j++) {

// Update the prefix[][]

if (j == 0)

prefix[i][j] = A[i][j];

else

prefix[i][j] = A[i][j]

+ prefix[i][j - 1];

}

}

// Store the maximum submatrix sum

int maxSum = Integer.MIN_VALUE;

// Iterate for starting column

for (int i = 0; i < c; i++) {

// Iterate for last column

for (int j = i; j < c; j++) {

// To store current array

// elements

Vector<Integer> v = new Vector<Integer>();

// Traverse every row

for (int k = 0; k < r; k++) {

// Store the sum of the

// kth row

int el = 0;

// Update the prefix

// sum

if (i == 0)

el = prefix[k][j];

else

el = prefix[k][j]

- prefix[k][i - 1];

// Push it in a vector

v.add(el);

}

// Update the maximum

// overall sum

maxSum = Math.max(maxSum, kadane(v));

}

}

// Print the answer

System.out.print(maxSum+ "\n");

}

// Driver Code

public static void main(String[] args)

{

int [][]matrix = { { 0, -2, -7, 0 },

{ 9, 2, -6, 2 },

{ -4, 1, -4, 1 },

{ -1, 8, 0, -2 } };

// Function Call

maxSubmatrixSum(matrix);

}

}

// This code is contributed by 29AjayKumar

Python3

# Python3 program for the above approach

import sys

# Function to find maximum continuous

# maximum sum in the array

def kadane(v):

# Stores current and maximum sum

currSum = 0

maxSum = -sys.maxsize - 1

# Traverse the array v

for i in range(len(v)):

# Add the value of the

# current element

currSum += v[i]

# Update the maximum sum

if (currSum > maxSum):

maxSum = currSum

if (currSum < 0):

currSum = 0

# Return the maximum sum

return maxSum

# Function to find the maximum

# submatrix sum

def maxSubmatrixSum(A):

# Store the rows and columns

# of the matrix

r = len(A)

c = len(A[0])

# Create an auxiliary matrix

# Traverse the matrix, prefix

# and initialize it will all 0s

prefix = [[0 for i in range(c)]

for j in range(r)]

# Calculate prefix sum of all

# rows of matrix A[][] and

# store in matrix prefix[]

for i in range(r):

for j in range(c):

# Update the prefix[][]

if (j == 0):

prefix[i][j] = A[i][j]

else:

prefix[i][j] = A[i][j] + prefix[i][j - 1]

# Store the maximum submatrix sum

maxSum = -sys.maxsize - 1

# Iterate for starting column

for i in range(c):

# Iterate for last column

for j in range(i, c):

# To store current array

# elements

v = []

# Traverse every row

for k in range(r):

# Store the sum of the

# kth row

el = 0

# Update the prefix

# sum

if (i == 0):

el = prefix[k][j]

else:

el = prefix[k][j] - prefix[k][i - 1]

# Push it in a vector

v.append(el)

# Update the maximum

# overall sum

maxSum = max(maxSum, kadane(v))

# Print the answer

print(maxSum)

# Driver Code

matrix = [ [ 0, -2, -7, 0 ],

[ 9, 2, -6, 2 ],

[ -4, 1, -4, 1 ],

[ -1, 8, 0, -2 ] ]

# Function Call

maxSubmatrixSum(matrix)

# This code is contributed by rag2127

C#

// C# program for the above approach

using System;

using System.Collections.Generic;

public class GFG{

// Function to find maximum continuous

// maximum sum in the array

static int kadane(List<int> v)

{

// Stores current and maximum sum

int currSum = 0;

int maxSum = int.MinValue;

// Traverse the array v

for (int i = 0;

i < (int)v.Count; i++)

{

// Add the value of the

// current element

currSum += v[i];

// Update the maximum sum

if (currSum > maxSum)

{

maxSum = currSum;

}

if (currSum < 0)

{

currSum = 0;

}

}

// Return the maximum sum

return maxSum;

}

// Function to find the maximum

// submatrix sum

static void maxSubmatrixSum(int [,]A)

{

// Store the rows and columns

// of the matrix

int r = A.GetLength(0);

int c = A.GetLength(1);

// Create an auxiliary matrix

int [,]prefix = new int[r,c];

// Traverse the matrix, prefix

// and initialize it will all 0s

for (int i = 0; i < r; i++) {

for (int j = 0; j < c; j++) {

prefix[i,j] = 0;

}

}

// Calculate prefix sum of all

// rows of matrix [,]A and

// store in matrix prefix[]

for (int i = 0; i < r; i++) {

for (int j = 0; j < c; j++) {

// Update the prefix[,]

if (j == 0)

prefix[i,j] = A[i,j];

else

prefix[i,j] = A[i,j]

+ prefix[i,j - 1];

}

}

// Store the maximum submatrix sum

int maxSum = int.MinValue;

// Iterate for starting column

for (int i = 0; i < c; i++) {

// Iterate for last column

for (int j = i; j < c; j++) {

// To store current array

// elements

List<int> v = new List<int>();

// Traverse every row

for (int k = 0; k < r; k++) {

// Store the sum of the

// kth row

int el = 0;

// Update the prefix

// sum

if (i == 0)

el = prefix[k,j];

else

el = prefix[k,j]

- prefix[k,i - 1];

// Push it in a vector

v.Add(el);

}

// Update the maximum

// overall sum

maxSum = Math.Max(maxSum, kadane(v));

}

}

// Print the answer

Console.Write(maxSum+ "\n");

}

// Driver Code

public static void Main(String[] args)

{

int [,]matrix = { { 0, -2, -7, 0 },

{ 9, 2, -6, 2 },

{ -4, 1, -4, 1 },

{ -1, 8, 0, -2 } };

// Function Call

maxSubmatrixSum(matrix);

}

}

// This code is contributed by 29AjayKumar

Javascript

<script>

// Javascript program for the above approach

// Function to find maximum continuous

// maximum sum in the array

function kadane(v)

{

// Stores current and maximum sum

let currSum = 0;

let maxSum = Number.MIN_VALUE;

// Traverse the array v

for (let i = 0;

i < v.length; i++)

{

// Add the value of the

// current element

currSum += v[i];

// Update the maximum sum

if (currSum > maxSum)

{

maxSum = currSum;

}

if (currSum < 0)

{

currSum = 0;

}

}

// Return the maximum sum

return maxSum;

}

// Function to find the maximum

// submatrix sum

function maxSubmatrixSum(A)

{

// Store the rows and columns

// of the matrix

let r = A.length;

let c = A[0].length;

// Create an auxiliary matrix

let prefix = new Array(r);

// Traverse the matrix, prefix

// and initialize it will all 0s

for (let i = 0; i < r; i++) {

prefix[i] = new Array(c);

for (let j = 0; j < c; j++) {

prefix[i][j] = 0;

}

}

// Calculate prefix sum of all

// rows of matrix A[][] and

// store in matrix prefix[]

for (let i = 0; i < r; i++) {

for (let j = 0; j < c; j++) {

// Update the prefix[][]

if (j == 0)

prefix[i][j] = A[i][j];

else

prefix[i][j] = A[i][j]

+ prefix[i][j - 1];

}

}

// Store the maximum submatrix sum

let maxSum = Number.MIN_VALUE;

// Iterate for starting column

for (let i = 0; i < c; i++) {

// Iterate for last column

for (let j = i; j < c; j++) {

// To store current array

// elements

let v = [];

// Traverse every row

for (let k = 0; k < r; k++) {

// Store the sum of the

// kth row

let el = 0;

// Update the prefix

// sum

if (i == 0)

el = prefix[k][j];

else

el = prefix[k][j]

- prefix[k][i - 1];

// Push it in a vector

v.push(el);

}

// Update the maximum

// overall sum

maxSum = Math.max(maxSum, kadane(v));

}

}

// Print the answer

document.write(maxSum+ "<br>");

}

// Driver Code

let matrix=[[ 0, -2, -7, 0 ],

[ 9, 2, -6, 2 ],

[ -4, 1, -4, 1 ],

[ -1, 8, 0, -2 ]];

// Function Call

maxSubmatrixSum(matrix);

// This code is contributed by unknown2108

</script>

Output:

15

Time Complexity: O(N3)
Auxiliary Space: O(N2)

Related Topic: Subarrays, Subsequences, and Subsets in Array



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