[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/

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。

 1 /**
 2  * @param {number} m
 3  * @param {number} n
 4  * @return {number}
 5  */
 6 var uniquePaths = function(m, n) {
 7     var i, j, count = 0, map = [];
 8     var len = Math.min(m, n);
 9     for(i = 0; i < m; i++){
10         map[i] = [];
11     }
12     for(i = 0; i < len; i++){
13         for(j = count; j < n; j++){
14             if(count === 0){
15                 map[count][j] = 1;
16             }else{
17                 map[count][j] = map[count - 1][j] + map[count][j - 1];
18             }
19         }
20         for(j = count + 1; j < m; j++){
21             if(count === 0){
22                 map[j][count] = 1;
23             }else{
24                 map[j][count] = map[j - 1][count] + map[j][count - 1];
25             }
26         }
27         count++;
28     }
29     return map[m - 1][n - 1];
30 };