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HDU 4585 Shaolin（STL map）
Description
When a young man passes all the tests and is declared a new monk of Shaolin, there will be a fight , as a part of the welcome party. Every monk has an unique id and a unique fighting grade, which are all integers. The new monk must fight with a old monk whose fighting grade is closest to his fighting grade. If there are two old monks satisfying that condition, the new monk will take the one whose fighting grade is less than his.
The master is the first monk in Shaolin, his id is 1，and his fighting grade is 1,000,000,000.He just lost the fighting records. But he still remembers who joined Shaolin earlier, who joined later. Please recover the fighting records for him.
Input
In each test case:
The first line is a integer n (0 <n <=100,000),meaning the number of monks who joined Shaolin after the master did.(The master is not included).Then n lines follow. Each line has two integer k and g, meaning a monk‘s id and his fighting grade.( 0<= k ,g<=5,000,000)
The monks are listed by ascending order of jointing time.In other words, monks who joined Shaolin earlier come first.
The input ends with n = 0.
Output
Sample Input
3 2 1 3 3 4 2 0
Sample Output
2 1 3 2 4 2
大致题意：很久以前，少林寺里只有一个等级10^9为方丈，他编号为1，少林寺里有个规矩，每个新来的和尚都必须和一位等级最接近自己的老（就是比他先来的）和尚进行战斗，后来又来了n个和尚，并且他们按入寺时间依次编号2~n+1，但是时间太久，方丈已经不知道每个和尚来的时候是跟哪个和尚战斗了，但是他还是记得哪个和尚比哪个和尚先来的。输入给出n个和尚的编号和他们的等级。下面就靠你了，让你依次求出每个和尚进寺是是跟谁战斗的，并输出。
解题思路：直接开数组的话，每次找跟他等级最接近的肯定要排序，目前知道的最快的快排的也是O(n*lg n)的，由于数据给的是10^5，再加上还要操作，时间已经超了。所以，得换个思路，那就得用到STL中的map的优势了，也好久没用map做题了。map里的数据会自动按键值升序排列，据说map内部的排序是用红黑树（一种不明觉厉的数据结构）实现的，其时间复杂度是O（n）的，同时，map里还可以直接用find（）按键值查找键值所在的迭代器，这就太方便了。
具体实现步骤：1.先开个map<int, int> monk, 把方丈的编号id和等级grad在map里建立映射，这里用到了一个小细节，
建立映射可以直接这样写，monk[grad] = id.
2.在循环输入n个和尚的信息，
1）每次输入一个和尚的信息，然后在map里建立映射；
2）此时用find（grad）寻找当前加入的和尚所在的迭代器；
3）然后，考虑当前的迭代器的位置，若是最后一个，就直接输出当前迭代器的前一个；
要是第一个，就输出当前迭代器的后面一个；
要既不是第一个也不是最后一个的话，就比较当前迭代器的first和它前后两迭代器first之间的差值哪个更小，小的输出；
要是两差值一样的话，输出前一个迭代器。
AC代码：
#include <stdio.h>
#include <string.h>
#include <iostream>
#include <algorithm>
#include <vector>
#include <queue>
#include <set>
#include <map>
#include <string>
#include <math.h>
#include <stdlib.h>
#include <time.h>
using namespace std;
#define INF 0x7fffffff
map<int, int> a; //声明一个map对象
int main()
{
#ifdef sxk
freopen("in.txt","r",stdin);
#endif
int n, k, g;
while(scanf("%d",&n)!=EOF && n)
{
a[1e9] = 1; //处理方丈
for(int i=0; i<n; i++){
scanf("%d%d", &k, &g);
a[g] = k;
map<int, int>::iterator temp = a.find(g); //按grad查找当前和尚所在的迭代器
if(temp == a.begin()) printf("%d %d\n", k, (++temp)->second);
else if(temp == a.end()) printf("%d %d\n", k, (--temp)->second);
else{
if(abs((--temp)->first - (++temp)->first) > abs((++temp)->first - (--temp)->first))
printf("%d %d\n", k, (++temp)->second);
else printf("%d %d\n", k, (--temp)->second);
}
}
a.clear();
}
return 0;
}
HDU 4585 Shaolin（STL map）