记忆化搜索——POJ 1088

对应POJ题目：点击打开链接

Description

 1  2  3  4 5

16 17 18 19 6

15 24 25 20 7

14 23 22 21 8

13 12 11 10 9

Input

Output

Sample Input

5 5
1 2 3 4 5
16 17 18 19 6
15 24 25 20 7
14 23 22 21 8
13 12 11 10 9

Sample Output

25

思路：枚举搜索每个点，直接搜会超时，当找到一个的最大长度，用mark[i][j] 记录下来，下次再遇到这个点，就直接取数！

#include<cstdio>
#include<cstdlib>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define M 100
int G[M][M];
int vis[M][M];
int mark[M][M];
int r, c;

void Dfs(int i, int j, int &step, int &max_step)
{
	if(vis[i][j] || i < 0 || i == r || j < 0 || j == c) return;
	if(mark[i][j]){ /* 如果走到了当前位置，则不需要再往下递归，因为此值已记录过，直接加上就行了 */
		step += mark[i][j];
		if(step > max_step) max_step = step;
		step -= mark[i][j];
		vis[i][j] = 0;
		return;
	}
	vis[i][j] = 1;
	int base = G[i][j];
	step++;
	if(G[i+1][j] < base) Dfs(i + 1, j, step, max_step);
	if(G[i-1][j] < base) Dfs(i - 1, j, step, max_step);
	if(G[i][j+1] < base) Dfs(i, j + 1, step, max_step);
	if(G[i][j-1] < base) Dfs(i, j - 1, step, max_step);
	if(step > max_step) max_step = step;
	step--; 
	vis[i][j] = 0;
	return;
}

int main()
{
	//freopen("in.txt","r",stdin);
	while(~scanf("%d%d", &r, &c))
	{
		memset(mark, 0, sizeof(mark));
		int i, j;
		for(i=0; i<r; i++)
			for(j=0; j<c; j++)
				scanf("%d", &G[i][j]);
		int max_step = 0;
		int step = 0;
		for(i=0; i<r; i++){
			for(j=0; j<c; j++){
				memset(vis, 0, sizeof(vis));
				int m = 0;
				Dfs(i, j, step, m);
				mark[i][j] = m; /* 记录从点G[i,j]开始的最长距离 */
				if(m > max_step) max_step = m;
			}
		}
		printf("%d\n", max_step);
	}
	return 0;
}

记忆化搜索——POJ 1088

原文：http://blog.csdn.net/u013351484/article/details/44263159