[LeetCode][JavaScript]Unique Paths

Unique Paths

A robot is located at the top-left corner of a m x n grid (marked 'Start' in the diagram below).

The robot can only move either down or right at any point in time. The robot is trying to reach the bottom-right corner of the grid (marked 'Finish' in the diagram below).

How many possible unique paths are there?

Above is a 3 x 7 grid. How many possible unique paths are there?

Note: m and n will be at most 100.

https://leetcode.com/problems/unique-paths/

 

 

 

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地图中没有障碍，而且只能往下和往右走。

当前格值就是上方的值加上左边的值，注意到要从左上往右下算，因为只能往右和往下走。

/**
 * @param {number} m
 * @param {number} n
 * @return {number}
 */
var uniquePaths = function(m, n) {
    var i, j, map = [];
    var len = Math.min(m, n);
    for(i = 0; i < m; i++){
        map[i] = [];
    }
    for(i = 0; i < len; i++){
        for(j = i; j < n; j++){
            if(i === 0){
                map[i][j] = 1;
            }else{
                map[i][j] = map[i - 1][j] + map[i][j - 1];
            }
        }
        for(j = i + 1; j < m; j++){
            if(i === 0){
                map[j][i] = 1;
            }else{
                map[j][i] = map[j - 1][i] + map[j][i - 1];
            }
        }
    }
    return map[m - 1][n - 1];
};