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Minimum number of flips required such that the last cell of matrix can be reached from any other cell
• Last Updated : 21 Apr, 2021

Given a matrix arr[][] of dimensions N * M where each cell consists of characters ‘R’ or ‘D’ except the cell arr[N][M] which contains ‘F’. ‘R’ and ‘D’ denotes that the player can move in the right and down direction respectively from the current cell. The task is to find the minimum number of characters required to be flipped from ‘R’ to ‘D’ or ‘D’ to ‘R’ such that it is possible to reach the finishing cell i.e., arr[N][M] from every cell.

Examples:

Input: N = 2, M = 3, arr[][] = {{D, D, R}, {R, R, F}}
Output: 1
Explanation: After changing the direction of (1, 3) to ‘D’, each cell can reach the finishing point.

Input: N = 1, M = 3, arr = {{D, D, F}}
Output: 2

Approach: The problem can be solved by observing that each cell can reach the finishing point after changing the following cells:

• Change all the ‘D’s to ‘R’ in the last row.
• Change all the ‘R’ to ‘D’ in the last column.

Follow the steps below to solve the problem:

1. Initialize a variable, say ans, to store the minimum number of flips.
2. Traverse from i = 0 to N – 1 and count the number of cells arr[i][M-1] which contains ‘R’.
3. Traverse from i = 0 to M – 1 and count the number of cells arr[N – 1][i] which contains ‘D’.
4. Print the sum of the two counts obtained in the above step as the required answer.

Below is the implementation of the above approach:

## C++

 `// C++ program for the above approach` `#include ``using` `namespace` `std;` `// Function to calculate the minimum``// number of flips required``int` `countChanges(vector > mat)``{``    ``// Dimensions of mat[][]``    ``int` `n = mat.size();``    ``int` `m = mat.size();` `    ``// Initialize answer``    ``int` `ans = 0;` `    ``// Count all 'D's in the last row``    ``for` `(``int` `j = 0; j < m - 1; j++) {``        ``if` `(mat[n - 1][j] != ``'R'``)``            ``ans++;``    ``}` `    ``// Count all 'R's in the last column``    ``for` `(``int` `i = 0; i < n - 1; i++) {``        ``if` `(mat[i][m - 1] != ``'D'``)``            ``ans++;``    ``}` `    ``// Print answer``    ``return` `ans;``}` `// Driver Code``int` `main()``{``    ``// Given matrix``    ``vector > arr = { { ``'R'``, ``'R'``, ``'R'``, ``'D'` `},``                                  ``{ ``'D'``, ``'D'``, ``'D'``, ``'R'` `},``                                  ``{ ``'R'``, ``'D'``, ``'R'``, ``'F'` `} };` `    ``// Function call``    ``int` `cnt = countChanges(arr);` `    ``// Print answer``    ``cout << cnt << endl;` `    ``return` `0;``}`

## Java

 `// Java program for the above approach``import` `java.io.*;` `class` `GFG{``    ` `// Function to calculate the minimum``// number of flips required    ``public` `static` `int` `countChanges(``char` `mat[][])``{``    ` `    ``// Dimensions of mat[][]``    ``int` `n = mat.length;``    ``int` `m = mat[``0``].length;` `    ``// Initialize answer``    ``int` `ans = ``0``;` `    ``// Count all 'D's in the last row``    ``for``(``int` `j = ``0``; j < m - ``1``; j++)``    ``{``        ``if` `(mat[n - ``1``][j] != ``'R'``)``            ``ans++;``    ``}` `    ``// Count all 'R's in the last column``    ``for``(``int` `i = ``0``; i < n - ``1``; i++)``    ``{``        ``if` `(mat[i][m - ``1``] != ``'D'``)``            ``ans++;``    ``}``    ` `    ``// Print answer``    ``return` `ans;``}` `// Driver Code``public` `static` `void` `main(String[] args)``{``    ``char` `arr[][] = { { ``'R'``, ``'R'``, ``'R'``, ``'D'` `},``                     ``{ ``'D'``, ``'D'``, ``'D'``, ``'R'` `},``                     ``{ ``'R'``, ``'D'``, ``'R'``, ``'F'` `} };` `    ``// Function call``    ``int` `cnt = countChanges(arr);` `    ``// Print answer``    ``System.out.println(cnt);``}``}` `// This code is contributed by Manu Pathria`

## Python3

 `# Python3 program for the above approach`` ` `# Function to calculate the minimum``# number of flips required``def` `countChanges(mat):``    ` `    ``# Dimensions of mat[][]``    ``n ``=` `len``(mat)``    ``m ``=` `len``(mat[``0``])`` ` `    ``# Initialize answer``    ``ans ``=` `0`` ` `    ``# Count all 'D's in the last row``    ``for` `j ``in` `range``(m ``-` `1``):``        ``if` `(mat[n ``-` `1``][j] !``=` `'R'``):``            ``ans ``+``=` `1``            ` `    ``# Count all 'R's in the last column``    ``for` `i ``in` `range``(n ``-` `1``):``        ``if` `(mat[i][m ``-` `1``] !``=` `'D'``):``            ``ans ``+``=` `1` `    ``# Print answer``    ``return` `ans` `# Driver Code` `# Given matrix``arr ``=` `[ [ ``'R'``, ``'R'``, ``'R'``, ``'D'` `] ,``        ``[ ``'D'``, ``'D'``, ``'D'``, ``'R'` `],``        ``[ ``'R'``, ``'D'``, ``'R'``, ``'F'` `] ]`` ` `# Function call``cnt ``=` `countChanges(arr)`` ` `# Print answer   ``print``(cnt)` `# This code is contributed by susmitakundugoaldanga`

## C#

 `// C# program for the above approach``using` `System;` `class` `GFG{``    ` `// Function to calculate the minimum``// number of flips required    ``public` `static` `int` `countChanges(``char` `[,]mat)``{``    ` `    ``// Dimensions of [,]mat``    ``int` `n = mat.GetLength(0);``    ``int` `m = mat.GetLength(1);``    ` `    ``// Initialize answer``    ``int` `ans = 0;``    ` `    ``// Count all 'D's in the last row``    ``for``(``int` `j = 0; j < m - 1; j++)``    ``{``        ``if` `(mat[n - 1,j] != ``'R'``)``            ``ans++;``    ``}` `    ``// Count all 'R's in the last column``    ``for``(``int` `i = 0; i < n - 1; i++)``    ``{``        ``if` `(mat[i,m - 1] != ``'D'``)``            ``ans++;``    ``}``    ` `    ``// Print answer``    ``return` `ans;``}` `// Driver Code``public` `static` `void` `Main(String[] args)``{``    ``char` `[,]arr = { { ``'R'``, ``'R'``, ``'R'``, ``'D'` `},``                    ``{ ``'D'``, ``'D'``, ``'D'``, ``'R'` `},``                    ``{ ``'R'``, ``'D'``, ``'R'``, ``'F'` `} };` `    ``// Function call``    ``int` `cnt = countChanges(arr);` `    ``// Print answer``    ``Console.WriteLine(cnt);``}``}` `// This code is contributed by Princi Singh`

## Javascript

 ``
Output:
`2`

Time Complexity: O(N*M)
Auxiliary Space: O(N*M)

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