Unique Paths in a Grid

• Time : $O(nm)$
• Space : $O(nm)$

int Solution::uniquePathsWithObstacles(vector<vector<int> > &A) {
    if(A[0][0] == 1) return 0;
    int n = A.size(), m = A[0].size();
    if(A[n-1][m-1] == 1) return 0;
    vector<vector<int>> dp(n + 1, vector<int>(m + 1,0));
    dp[0][0] = 1;
    for(int i = 0; i < n; i++) {
        for(int j = 0; j < m; j++) {
            if(A[i][j]) continue;
            dp[i+1][j] += dp[i][j];
            dp[i][j+1] += dp[i][j];
        }
    }
    return dp[n-1][m-1];
}