/*
Runtime: 0 ms, faster than 100.00% of Java online submissions for Unique Paths.
Memory Usage: 33.1 MB, less than 5.10% of Java online submissions for Unique Paths.
*/
class Solution {
    public int uniquePaths(int m, int n) {
        if (m < 1 || n < 1) return 0;
        int[][] p = new int[m][n];
        for(int j=0; j<n; ++j){
            p[0][j] = 1;
        }
        for(int i=1; i<m; ++i){
            p[i][0] = 1;
            for(int j=1; j<n; ++j){
                p[i][j] = p[i-1][j]+p[i][j-1];
            }
        }
        return p[m-1][n-1];
    }
}