[62] 不同路径

/**
 * @param {number} m
 * @param {number} n
 * @return {number}
 */
var uniquePaths = function (m, n) {
    // n 行 m列
    const matrix = Array.from(Array(m), item => new Array(n).fill(0))
    matrix[0] = new Array(n).fill(1);
    for (let i = 0; i < m; i++) {
        matrix[i][0] = 1;
    }
    for (let i = 1; i < m; i++) {
        for (let j = 1; j < n; j++) {
            matrix[i][j] = matrix[i - 1][j] + matrix[i][j - 1]
        }
    }
    return matrix[m - 1][n - 1];
};