int uniquePathsWithObstacles(vector<vector<int>>& obstacleGrid) {

int m = obstacleGrid.size(), n = obstacleGrid[0].size();

if (obstacleGrid[0][0]) return 0;

for(int i = 0; i < m; ++i) {

for (int j = 0; j < n; ++j) {

if (obstacleGrid[i][j]) {

obstacleGrid[i][j] = 0;

} else {

if (i == 0 && j == 0) {

obstacleGrid[i][j] = 1;

} else if (i == 0) {

obstacleGrid[i][j] = obstacleGrid[i][j-1];

} else if (j == 0) {

obstacleGrid[i][j] = obstacleGrid[i-1][j];

} else {

obstacleGrid[i][j] = obstacleGrid[i][j-1] + obstacleGrid[i-1][j];

}

}

}

}

return obstacleGrid.back().back();

}