[63] 不同路径 II

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

            }
        }
    }
    return matrix[m - 1][n - 1];
};