HDU 3743 Frosh Week_hdu - 3743-优快云博客

本文详细介绍了HDU 3743问题的求解策略，通过使用线段树优化区间更新和查询操作，提高了程序效率。包括数据结构设计、算法实现和代码解析。

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I can't understanding the problem's meaning.

The student's number of people is not from 1 to n.

Have multiply datas.

The portal:http://acm.hdu.edu.cn/showproblem.php?pid=3743

#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <iostream>
#include <algorithm>

using namespace std;

const int M = 1000005;

struct Node{
	int value,r;
}a[M];

int Bit[M << 1] ;

void Insert(int x,int value) {
	for(int i = x ; i < M ; i += i & (-i)) {
		Bit[i] += value;
	}
}

int Query(int x){
	int ret = 0;
	for(int i = x ; i  ; i -= i & (-i)) {
		ret += Bit[i];
	}
	return ret;
}

bool cmp(Node a1,Node a2){
	return (a1.value - a2.value) < 0;
}

void print(){
	for(int i=0 ; i<10 ; i++) {
		printf("%d %d\n",a[i].r,a[i].value);
	}
}

void Deal_with(){
	int n,tempx;
	while(~scanf("%d",&n)) {
		memset(Bit,0,sizeof(Bit));
		memset(a,0,sizeof(a));
		long long cnt = 0;
		for(int i = 0 ; i < n ; i ++ ) {
			scanf("%d",&a[i].value);
			a[i].r = i + 1;
		}
		sort(a,a+n,cmp);
		//print();
		for(int i = 0 ; i < n ; i ++ ) {
			cnt += i - Query(a[i].r);
			Insert(a[i].r,1);
		}
		printf("%lld\n",cnt);
	}
}

int main(void){
	//freopen("a.in","r",stdin);
	Deal_with();
	return 0;
}