Algorithms-64.Minimum Path Sum

思路：动态规划。f(x,y)=(x,y)+Min(f(x+1,y),f(x,y+1))，只是用这个递归会导致Time Limit Exceeded,再递归查询的同时建立一个hashmap，存储查询过的f(x,y)，避免重复查询。

public class Solution {    public int minPathSum(int[][] grid) {    int xl=grid.length;    int yl=grid[0].length;    Map<String, Integer> map=new HashMap<String, Integer>();    return f(grid,0,0,xl,yl,map);    }    public int f(int[][] grid,int x,int y,int xl,int yl,Map<String, Integer> map){    String coordinate=x+","+y;    if (map.get(coordinate)==null) {if (x>=xl||y>=yl) {return -1;}else {int xv=f(grid,x+1,y,xl,yl,map);int yv=f(grid,x,y+1,xl,yl,map);   int v=0;   if (xv<0) {v=yv;}else if (yv<0) {v=xv;}else if (xv>yv){v=yv;}else {v=xv;}int value=grid[x][y]+(v<0?0:v);map.put(coordinate, value);return value;}}    return map.get(coordinate);    }}

耗时：440ms，下游。