63. Unique Paths II

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class Solution {
public:
    int uniquePathsWithObstacles(vector<vector<int>>& obstacleGrid) {
        int m = obstacleGrid.size();
        int n = obstacleGrid[0].size();
        vector<vector<int>> dp(m);
        for(int i = 0; i < m; i++){
            dp[i].resize(n);
        }
        if(obstacleGrid[0][0] == 1 || obstacleGrid[m - 1][n  - 1] == 1) return 0;
        dp[0][0] = 1;
        for(int i = 0; i < m ; i++){
            for(int j = 0; j < n;j++){
                if(i == 0 & j == 0) continue;//一定要注意，不能把dp[0][0]设为0，否则全部都是0；
                int up = (i - 1 >= 0 && obstacleGrid[i - 1][j] == 0) ? dp[i - 1][j] : 0;
                int left = (j - 1 >= 0 && obstacleGrid[i][j - 1] == 0) ? dp[i][j - 1] : 0;
                dp[i][j] = up + left;
            }
        }
        return dp[m - 1][n - 1];
    }
};