LeetCode - Unique Paths

Unique Paths

//
public int uniquePaths(int m, int n) {
        if(m<1 || n<1) return 0;
        if(m==1 || n==1) return 1;
        int[][] ret = new int[m][n];
        
        for(int i=0; i<m; i++){
            ret[i][0] = 1;
        }
        
        for(int i=0; i<n; i++){
            ret[0][i] = 1;
        }
        
        for(int i=1; i<m; i++){
            for(int j=1; j<n; j++){
                ret[i][j] = ret[i-1][j] + ret[i][j-1];
            }
        }
        return ret[m-1][n-1];
    }
// better solution: less space complexity
public int uniquePaths(int m, int n) {
        if(m<=0 || n<=0)
            return 0;
        int[] res = new int[n];
        res[0] = 1;
        for(int i=0;i<m;i++)
        {
            for(int j=1;j<n;j++)
            {
               res[j] += res[j-1];
            }
        }
        return res[n-1];
    }