Make Matrix Beautiful

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Time: O(n*m)

Space: O(n+m)

Intuition

Make all rows and columns have same sum with minimum increment operations.

Algorithm

1Target = max of all row sums and column sums. For each row: increment elements to reach target. Adjust columns accordingly.

Common Pitfalls

•Target is max(maxRowSum, maxColSum). Fill row by row; recalculate column sums. Total ops = n*target - sum(all elements).

Make Matrix Beautiful.java

Java

// Approach: Find each row and column max, then ensure every row/column sums to the global max.
// Time: O(n*m) Space: O(n+m)
class Solution {
    public static int balanceSums(int[][] mat) {
        int n = mat.length;

        int[] rowSum = new int[n];
        int[] colSum = new int[n];

        // Calculate row and column sums
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < n; j++) {
                rowSum[i] += mat[i][j];
                colSum[j] += mat[i][j];
            }
        }

        // Find the maximum sum among all row sums and column sums
        int maxSum = 0;
        for (int i = 0; i < n; i++) {
            maxSum = Math.max(maxSum, rowSum[i]);
            maxSum = Math.max(maxSum, colSum[i]);
        }

        // To make matrix beautiful, we need to make all row and column sums equal to
        // maxSum
        int operations = 0;
        for (int i = 0; i < n; i++)
            operations += maxSum - rowSum[i]; // Only row difference is enough since total increase should balance
                                              // column as well

        return operations;
    }
}

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