Path with maximum average value

2.1

Given a square matrix of size N*N, where each cell is associated with a specific cost. A path is defined as a specific sequence of cells which starts from top left cell move only right or down and ends on bottom right cell. We want to find a path with maximum average over all existing paths. Average is computed as total cost divided by number of cells visited in path.
Examples:

Input : Matrix = [1, 2, 3
                  4, 5, 6
                  7, 8, 9]
Output : 5.8
Path with maximum average is, 1 -> 4 -> 7 -> 8 -> 9
Sum of the path is 29 and average is 29/5 = 5.8

One interesting observation is, the only allowed moves are down and right, we need N-1 down moves and N-1 right moves to reach destination (bottom rightmost). So any path from from top left corner to bottom right corner requires 2N – 1 cells. In average value, denominator is fixed and we need to just maximize numerator. Therefore we basically need to to find maximum sum path. Calculating maximum sum of path is a classic dynamic programming problem, if dp[i][j] represents maximum sum till cell (i, j) from (0, 0) then at each cell (i, j), we update dp[i][j] as below,

for all i, 1 <= i <= N
   dp[i][0] = dp[i-1][0] + cost[i][0];    
for all j, 1 <= j <= j
   dp[0][j] = dp[0][j-1] + cost[0][j];            
otherwise    
   dp[i][j] = max(dp[i-1][j], dp[i][j-1]) + cost[i][j]; 

Once we get maximum sum of all paths we will divide this sum by (2N – 1) and we will get our maximum average.

C++

//    C/C++ program to find maximum average cost path
#include <bits/stdc++.h>
using namespace std;

// Maximum number of rows and/or columns
const int M = 100;

// method returns maximum average of all path of
// cost matrix
double maxAverageOfPath(int cost[M][M], int N)
{
    int dp[N+1][N+1];
    dp[0][0] = cost[0][0];

    /* Initialize first column of total cost(dp) array */
    for (int i = 1; i < N; i++)
        dp[i][0] = dp[i-1][0] + cost[i][0];

    /* Initialize first row of dp array */
    for (int j = 1; j < N; j++)
        dp[0][j] = dp[0][j-1] + cost[0][j];

    /* Construct rest of the dp array */
    for (int i = 1; i < N; i++)
        for (int j = 1; j <= N; j++)
            dp[i][j] = max(dp[i-1][j],
                          dp[i][j-1]) + cost[i][j];

    // divide maximum sum by constant path
    // length : (2N - 1) for getting average
    return (double)dp[N-1][N-1] / (2*N-1);
}

/* Driver program to test above functions */
int main()
{
    int cost[M][M] = { {1, 2, 3},
        {6, 5, 4},
        {7, 3, 9}
    };
    printf("%f", maxAverageOfPath(cost, 3));
    return 0;
}

Java

// JAVA Code for Path with maximum average
// value
class GFG {
    
    // method returns maximum average of all
    // path of cost matrix
    public static double maxAverageOfPath(int cost[][],
                                               int N)
    {
        int dp[][] = new int[N+1][N+1];
        dp[0][0] = cost[0][0];
     
        /* Initialize first column of total cost(dp)
           array */
        for (int i = 1; i < N; i++)
            dp[i][0] = dp[i-1][0] + cost[i][0];
     
        /* Initialize first row of dp array */
        for (int j = 1; j < N; j++)
            dp[0][j] = dp[0][j-1] + cost[0][j];
     
        /* Construct rest of the dp array */
        for (int i = 1; i < N; i++)
            for (int j = 1; j < N; j++)
                dp[i][j] = Math.max(dp[i-1][j],
                           dp[i][j-1]) + cost[i][j];
     
        // divide maximum sum by constant path
        // length : (2N - 1) for getting average
        return (double)dp[N-1][N-1] / (2 * N - 1);
    }
    
    /* Driver program to test above function */
    public static void main(String[] args) 
    {
        int cost[][] = {{1, 2, 3},
                        {6, 5, 4},
                        {7, 3, 9}};
                
        System.out.println(maxAverageOfPath(cost, 3));
    }
}
// This code is contributed by Arnav Kr. Mandal.


Output:

5.2

This article is contributed by Utkarsh Trivedi. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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