LeetCode 63.Unique Paths II

题目：

Follow up for "Unique Paths":

Now consider if some obstacles are added to the grids. How many unique paths would there be?

An obstacle and empty space is marked as 1 and 0 respectively in the grid.

For example,

There is one obstacle in the middle of a 3x3 grid as illustrated below.

[  [0,0,0],  [0,1,0],  [0,0,0]]

The total number of unique paths is 2.

Note: m and n will be at most 100.

分析与解答：

只能DP了，我用了二维数组，其实一维就可以的。

class Solution {public:    int uniquePathsWithObstacles(vector<vector<int> > &obstacleGrid) {        if(obstacleGrid.empty() || obstacleGrid[0].empty()){             return 0;        }        size_t m = obstacleGrid.size(),n = obstacleGrid[0].size();//m行n列        if(obstacleGrid[m-1][n-1]==1){            return 0;        }        vector<vector<int> > dp(m+1,vector<int>(n+1,0));        int maxnum = m + n;        dp[m][n] = 1;        for(int i = m;i>=1;--i){            for(int j=n;j>=1;--j){                if(i+j == maxnum){                    continue;                }                if(obstacleGrid[i-1][j-1] == 1){                    dp[i][j] = 0;                }else{                    dp[i][j] = (i+1>m?0:dp[i+1][j]) + (j+1>n?0:dp[i][j+1]);                }            }        }        return dp[1][1];    }};