62. Unique Paths（js）

62. 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 7 x 3 grid. How many possible unique paths are there?

Note: m and n will be at most 100.

Example 1:

Input: m = 3, n = 2
Output: 3
Explanation:
From the top-left corner, there are a total of 3 ways to reach the bottom-right corner:
1. Right -> Right -> Down
2. Right -> Down -> Right
3. Down -> Right -> Right

Example 2:

Input: m = 7, n = 3
Output: 28

题意：机器人只能向右或者向下移动，问有几种不同的走法

代码如下：

/**
 * @param {number} m
 * @param {number} n
 * @return {number}
 */
var uniquePaths = function(m, n) {
    var dp=[];
    dp[0]=1;
    for(var i=1;i<n;i++){
        dp[i]=null;
    }
    for(var i=0;i<m;i++){
        for(var j=0;j<n;j++){
            if(j>0)
                dp[j]+=dp[j-1]
        }
    }
    return dp[n-1];
};

62. Unique Paths

Medium