POJ 1054 搜索

Posted 2020-12-21 znk97

#include<iostream>
#include<memory.h>
#include<cmath>
#include<algorithm>
using namespace std;

typedef struct
{
    int x, y;
}node;

node d[6000];
int r, c;
int n;
bool map[6000][6000];
int ans = 0;

bool cmp(node a, node b)
{
    if(a.y == b.y) return a.x<b.x;
    else return a.y<b.y;
}

void solve()
{
    for(int i = 0; i < n; i++)
    {
        for(int j = i+1; j < n; j++) 
        {   
            int x = d[i].x, y = d[i].y;
            int vx = d[j].x-d[i].x, vy = d[j].y-d[i].y;

            if(y+ans*vy > c) break; //剪枝
            if(x+ans*vx > r) continue;  //后面的 x 可能比前面的小，所以用continue
            if(ans == (r>c?r:c)) return;   //剪枝

            if(x-vx >= 1 && x-vx <= r && y-vy >= 1 && y-vy <= c) continue;  //前面的点在图内

            int d = 2;
            while(x+d*vx >= 1 && x+d*vx <= r && y+d*vy >= 1 && y+d*vy <= c && map[x+d*vx][y+d*vy]) d++;
            if(d >= 3)
                if(x+d*vx < 1 || x+d*vx > r || y+d*vy < 1 || y+d*vy > c)
                    ans = d>ans ? d:ans;
            
        }
    }
}

int main()
{
    cin >> r >> c;
    cin >> n;
    memset(map, false, sizeof map);

    for(int i = 0; i < n; i++)
    {
        cin >> d[i].x >> d[i].y;
        map[d[i].x][d[i].y] = true;
    }
    sort(d, d+n, cmp);  //预先排序

    solve();
    cout << ans;
    system("pause");
    return 0;
}