# Maximum sum path in a matrix from top to bottom in C++

C++Server Side ProgrammingProgramming

## Problem statement

Consider a n*n matrix. Suppose each cell in the matrix has a value assigned. We can go from each cell in row i to a diagonally higher cell in row i+1 only [i.e from cell(i, j) to cell(i+1, j-1) and cell(i+1, j+1) only]. Find the path from the top row to the bottom row following the aforementioned condition such that the maximum sum is obtained

## Example

If given input is:
{
{5, 6, 1, 17},
{-2, 10, 8, -1},
{ 3, -7, -9, 4},
{12, -4, 2, 2}
}

the maximum sum is (17 + 8 + 4 + 2) = 31

## Algorithm

• The idea is to find maximum sum, or all paths starting with every cell of first row and finally return maximum of all values in first row.

• We use Dynamic Programming as results of many sub problems are needed again and again

## Example

Live Demo

#include <bits/stdc++.h>
using namespace std;
#define SIZE 10
int getMaxMatrixSum(int mat[SIZE][SIZE], int n){
if (n == 1) {
return mat[0][0];
}
int dp[n][n];
int maxSum = INT_MIN, max;
for (int j = 0; j < n; j++) {
dp[n - 1][j] = mat[n - 1][j];
}
for (int i = n - 2; i >= 0; i--) {
for (int j = 0; j < n; j++) {
max = INT_MIN;
if (((j - 1) >= 0) && (max < dp[i + 1][j - 1])) {
max = dp[i + 1][j - 1];
}
if (((j + 1) < n) && (max < dp[i + 1][j + 1])) {
max = dp[i + 1][j + 1];
}
dp[i][j] = mat[i][j] + max;
}
}
for (int j = 0; j < n; j++) {
if (maxSum < dp[0][j]) {
maxSum = dp[0][j];
}
}
return maxSum;
}
int main(){
int mat[SIZE][SIZE] = {
{5, 6, 1, 17},
{-2, 10, 8, -1},
{3, -7, -9, 4},
{12, -4, 2, 2}
};
int n = 4;
cout << "Maximum Sum = " << getMaxMatrixSum(mat, n) << endl;
return 0;
}

## Output

When you compile and execute above program. It generates following output−

Maximum Sum = 31
Published on 30-Jan-2020 12:41:27