不同路径

动态规划

1. 
   ```javascript var uniquePaths = function (m, n) { const f = new Array(m).fill(0).map(() => new Array(n).fill(0));

   for (let i = 0; i < m; i++) { f[i][0] = 1; } for (let j = 0; j < n; j++) { f[0][j] = 1; }

   for (let i = 1; i < m; i++) { for (let j = 1; j < n; j++) { // 可以从两个方向走来 f[i][j] = f[i - 1][j] + f[i][j - 1]; } } // 从 0 开始算，所以还要-1 return f[m - 1][n - 1]; };

<a name="I3xHq"></a>
### 排列组合？
```javascript
var uniquePaths = function(m, n) {
    let ans = 1;
    for (let x = n, y = 1; y < m; ++x, ++y) {
        ans = Math.floor(ans * x / y);
    }
    return ans;
};