8-4 Fabled Rooks uva11134

　　题意：你的任务是在n*n的棋盘上放 n 小于5000 个车使得任意两个车不互相攻击且第i个车在一个给定的矩形ri之内给出该矩形左上角坐标和右下角坐标四个点必须满足放车的位置在矩形内边上也行如果无解输出IMPSSIBLE

行与列是独立的所以可以分割成两个一模一样的子问题贪心

要以右边界升序排序我一开始按照左边界排序错了举个例子 1-1 1-3 2-2 这样的话就会错 1-1 2-2 1-3才对

还有就是注意细节 sort 从一开始的话都要加一，，，

#include<bits/stdc++.h>
using namespace std;
#define N 5010
int n,k;
int vis[N];
struct node
{
    int id;
    int x,y;
    int x1,x2,y1,y2;

}chess[N];

bool cmp1(node a,node b)
  {
    return a.x2<b.x2||(a.x2==b.x2&&a.x1<b.x1);
  }
bool cmp2(node a,node b)
  {
   return a.y2<b.y2||(a.y2==b.y2&&a.y1<b.y1);
  }
bool cmp3(node a,node b)
   {
    return a.id<b.id;
   }
int main()
{
    while(cin>>n,n)
    {
        int flag=1;
        for(int i=0;i<n;i++)
        {
           chess[i].id=i;
           scanf("%d%d%d%d",&chess[i].x1,&chess[i].y1,&chess[i].x2,&chess[i].y2);
        }
        sort(chess,chess+n,cmp1);
        memset(vis,0,sizeof vis);

        for(int i=0;i<n;i++)
        {
            int ok=0;
            for(int j=chess[i].x1;j<=chess[i].x2;j++)
            {
                if(!vis[j]){ok=1;vis[j]=1;chess[i].x=j;break; }//把chess里面的i写成了j  强行将自己dubug了半个小时。。。
            }
            if(!ok){flag=0;}
        }
         sort(chess,chess+n,cmp2);
          memset(vis,0,sizeof vis);
         for(int i=0;i<n;i++)
        {
            int ok=0;
            for(int j=chess[i].y1;j<=chess[i].y2;j++)
            {
                if(!vis[j]){ok=1;vis[j]=1;chess[i].y=j;break; }
            }
            if(!ok){flag=0;}
        }
        sort(chess,chess+n,cmp3);
       if(flag)
        for(int i=0;i<n;i++)
            printf("%d %d\n",chess[i].x,chess[i].y);
       else printf("IMPOSSIBLE\n");
    }
}

LRJ的代码更慢

#include<cstdio>
#include<cstring>
#include <algorithm>
using namespace std;

// solve 1-D problem: find c so that a[i] <= c[i] <= b[i] (0 <= i < n)
bool solve(int *a, int *b, int *c, int n) {
  fill(c, c+n, -1);
  for(int col = 1; col <= n; col++) {
    // find a rook with smalleset b that is not yet assigned
    int rook = -1, minb = n+1;
    for(int i = 0; i < n; i++)
      if(c[i] < 0 && b[i] < minb && col >= a[i]) { rook = i; minb = b[i]; }
    if(rook < 0 || col > minb) return false;
    c[rook] = col;
  }
  return true;
}

const int maxn = 5000 + 5;
int n, x1[maxn], y1[maxn], x2[maxn], y2[maxn], x[maxn], y[maxn];

int main() {
  while(scanf("%d", &n) == 1 && n) {
    for (int i = 0; i < n; i++)
      scanf("%d%d%d%d", &x1[i], &y1[i], &x2[i], &y2[i]);
    if(solve(x1, x2, x, n) && solve(y1, y2, y, n))
      for (int i = 0; i < n; i++) printf("%d %d\n", x[i], y[i]);
    else
      printf("IMPOSSIBLE\n");
  }
  return 0;
}

8-4 Fabled Rooks uva11134

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