class Solution {
public:
int uniquePathsWithObstacles(std::vector<std::vector<int>>& obstacleGrid) {
int m = obstacleGrid.size(), n= obstacleGrid[0].size();
if (obstacleGrid[0][0]==1||obstacleGrid[m-1][n-1]==1) return 0;
std::vector<std::vector<int>> dp(m, std::vector<int>(n,0));
// 一旦obs[i][0]=0，for循环终止。对于for(1;2;3)里判断条件2是if而非while语句
for (int i=0;i<m && obstacleGrid[i][0]==0;i++) dp[i][0]=1;
for (int j=0;j<n && obstacleGrid[0][j]==0;j++) dp[0][j]=1;
for (int i=1;i<m;i++)
for (int j=1;j<n;j++)
if (obstacleGrid[i][j]==0) dp[i][j] = dp[i-1][j]+dp[i][j-1];
// 等价于if (obstacleGrid[i][j]==1) continue; dp[i][j] = dp[i-1][j]+dp[i][j-1];
return dp[m-1][n-1];
}
};