第四届河南省省赛 走迷宫 二分+DFS

#include<iostream>
#include<algorithm>
#include<cstring>
#include<vector>
#include<stdio.h>
#include<queue>
#include<math.h>
#define INF 0x3f3f3f3f
#define MAX 105

using namespace std;

int Map[MAX][MAX],vis[MAX][MAX],v[4][2]={{1,0},{-1,0},{0,1},{0,-1}},n;

bool check(int x,int y)
{
    if(x>=1 && x<=n && y>=1 && y<=n && !vis[x][y])
        return true;
    return false;
}

bool DFS(int x,int y,int maxn,int minn)//深搜，若搜索过程中未发现 超越minn 和 maxn的值则搜索成功
{
    if(x==n && y==n)
        return true;
    for(int i=0;i<4;i++)
    {
        int next_x=x+v[i][0];
        int next_y=y+v[i][1];
        if(check(next_x,next_y) && (Map[next_x][next_y]<=maxn && Map[next_x][next_y]>=minn))
        {
            vis[next_x][next_y]=1;
            if(DFS(next_x,next_y,maxn,minn))
                return true;
        }
    }
    return false;
}

int main()
{
    int L,R,Mid,maxn,minn,ans;
    while(scanf("%d",&n)!=EOF)
    {
        memset(Map,0,sizeof(Map));
        minn=INF;
        maxn=-INF;
        for(int i=1;i<=n;i++)
        {
            for(int j=1;j<=n;j++)
            {
                scanf("%d",&Map[i][j]);
                minn=min(minn,Map[i][j]);
                maxn=max(maxn,Map[i][j]);
            }
        }
        L=abs(Map[n][n]-Map[1][1]);//首尾你无法避免，所以将其差的绝对值定为最左端
        R=maxn-minn;
        while(L<=R)//对差值进行二分查找
        {
            Mid=(L+R)/2;
            int ok=0;
            for(int i=minn;i<=maxn-Mid;i++)
            {
                if(Map[1][1] < i)
                    break;
                if(Map[1][1] > i+Mid)
                    continue;
                memset(vis,0,sizeof(vis));
                if(DFS(1,1,i+Mid,i))
                {
                    ans=Mid;
                    R=Mid-1;
                    ok=1;
                    break;
                }
            }
            if(!ok)
                L=Mid+1;
        }
        printf("%d\n",ans);
    }
    return 0;
}