hihoCoder #1497 : Queen Attack

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本文介绍了一种使用C++和map数据结构解决国际象棋中皇后互相攻击问题的方法。通过记录每行、列及对角线上的皇后数量，快速计算出可能的攻击对数。

点击打开链接

时间限制: 10000ms

单点时限: 1000ms

内存限制: 256MB

描述

There are N queens in an infinite chessboard. We say two queens may attack each other if they are in the same vertical line, horizontal line or diagonal line even if there are other queens sitting between them.

Now given the positions of the queens, find out how many pairs may attack each other?

输入

The first line contains an integer N.

Then N lines follow. Each line contains 2 integers Ri and Ci indicating there is a queen in the Ri-th row and Ci-th column.

No two queens share the same position.

For 80% of the data, 1 <= N <= 1000

For 100% of the data, 1 <= N <= 100000, 0 <= Ri, Ci <= 1000000000

输出

One integer, the number of pairs may attack each other.

样例输入

样例输出

本来觉得题很复杂，看了一个大佬的博客，原来map可以这样用，受教了。以后的路还有好远。

#include<cstdio>
#include<cstring>
#include<iostream>
#include<cmath>
#include<cstdlib>
#include<map>
using namespace std;
#define ll long long
map<int,int>m1;
map<int,int>m2;
map<int,int>m3;
map<int,int>m4;
int main()
{
    int n,a,b,ans=0;
    scanf("%d",&n);
    for(int i=0;i<n;i++)
    {
        scanf("%d%d",&a,&b);
        ans+=m1[a];
        m1[a]++;
        ans+=m2[b];
        m2[b]++;
        ans+=m3[a+b];
        m3[a+b]++;
        ans+=m4[a-b];
        m4[a-b]++;
    }
    printf("%d\n",ans);
    return 0;
}