[leetcode]Unique Paths

动态规划。巧妙的是通过在最上和最左边加一条0的线，大大简化了编程实现。

public class Solution {
    public int uniquePaths(int m, int n) {
        // Start typing your Java solution below
        // DO NOT write main() function
        int[][] mx = new int[m+1][n+1];
        
        for (int i = 0; i < m+1; i++) {
            mx[i][0] = 0;
        }
        for (int i = 0; i < n+1; i++) {
            mx[0][i] = 0;
        }

        for (int i = 1; i < m+1; i++) {
            for (int j = 1; j < n+1; j++) {
                if (i == 1 && j == 1) mx[i][j] = 1;
                else mx[i][j] = mx[i-1][j] + mx[i][j-1];
            }
        }
        
        return mx[m][n];
    }
}