A k x k magic square is a k x k grid filled with integers such that every row sum, every column sum, and both diagonal sums are all equal. The integers in the magic square do not have to be distinct. Every 1 x 1 grid is trivially a magic square. Giv

largestMagicSquare.js

/**
 * @param {number[][]} grid
 * @return {number}
 */
var largestMagicSquare = function(grid) {
    const m = grid.length;
    const n = grid[0].length;

    // Helper: check if the k×k square starting at (r, c) is magic
    function isMagic(r, c, k) {
        // Compute the target sum using the first row
        let target = 0;
        for (let j = 0; j < k; j++) {
            target += grid[r][c + j];
        }

        // Check all row sums
        for (let i = 0; i < k; i++) {
            let rowSum = 0;
            for (let j = 0; j < k; j++) {
                rowSum += grid[r + i][c + j];
            }
            if (rowSum !== target) return false;
        }

        // Check all column sums
        for (let j = 0; j < k; j++) {
            let colSum = 0;
            for (let i = 0; i < k; i++) {
                colSum += grid[r + i][c + j];
            }
            if (colSum !== target) return false;
        }

        // Check main diagonal
        let diag1 = 0;
        for (let i = 0; i < k; i++) {
            diag1 += grid[r + i][c + i];
        }
        if (diag1 !== target) return false;

        // Check anti-diagonal
        let diag2 = 0;
        for (let i = 0; i < k; i++) {
            diag2 += grid[r + i][c + (k - 1 - i)];
        }
        if (diag2 !== target) return false;

        return true;
    }

    // Try sizes from largest to smallest
    const maxK = Math.min(m, n);
    for (let k = maxK; k >= 2; k--) {
        for (let r = 0; r + k <= m; r++) {
            for (let c = 0; c + k <= n; c++) {
                if (isMagic(r, c, k)) {
                    return k; // first valid k is the largest
                }
            }
        }
    }

    // If no k > 1 works, return 1
    return 1;
};