62. Unique Paths 自己写的一次ac

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.

class Solution {
public:
    int uniquePaths(int m, int n) {
        vector<vector<int>> vec;
        vector<int> tmp;
        if(m==0||n==0)return 0;
        if(m==1||n==1)return 1;
        for(int i=0;i<n;i++)
            tmp.push_back(0);
        for(int i=0;i<m;i++)
            vec.push_back(tmp);
        
        for(int i=m-1;i>=0;i--){
            for(int j=n-1;j>=0;j--){
                if(j==n-1){
                    vec[i][j]=1;
                }
                else if(i==m-1){
                    vec[i][j]=1;
                }
                else{
                    vec[i][j]=vec[i][j+1]+vec[i+1][j];
                }
            }
        }
        return vec[0][0];
    }
};