HDU 1754 I Hate It

最新推荐文章于 2020-09-30 13:33:24 发布

_NMfloat_

最新推荐文章于 2020-09-30 13:33:24 发布

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文章标签： acm HDU algorithm Segment Tree

本文链接：https://blog.youkuaiyun.com/NMfloat/article/details/46866801

本文介绍了段树的构建、更新和查询操作，通过实例详细解释了如何使用段树进行高效的区间最大值查找和更新。

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Simple segment tree;

The portal:http://acm.hdu.edu.cn/showproblem.php?pid=1754

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

using namespace std;

const int MAXN = 200005;

struct Node {
	int value;
	int Left;
	int Right;
}Segment_Tree[MAXN<<2];

int a[MAXN];
int cnt ;

void Build_Tree(int Left,int Right,int Now) {
	Segment_Tree[Now].Left = Left;
	Segment_Tree[Now].Right = Right;
	if(Left == Right) {
		Segment_Tree[Now].value = a[cnt++];
		return ;
	}
	int Mid = (Left + Right) >> 1;
	Build_Tree(Left,Mid,Now<<1);
	Build_Tree(Mid+1,Right,Now<<1|1);
	Segment_Tree[Now].value = max(Segment_Tree[Now<<1].value,Segment_Tree[Now<<1|1].value);
}

void Update_Tree(int Left,int Right,int Now,int position,int change_value) {
	if(Left == Right) {
		Segment_Tree[Now].value = change_value;
		return;
	}
	int Mid = (Left + Right) >> 1;
	if(position > Mid) {
		Update_Tree(Mid+1,Right,Now<<1|1,position,change_value);
	}
	else {
		Update_Tree(Left,Mid,Now<<1,position,change_value);
	}
	Segment_Tree[Now].value = max(Segment_Tree[Now<<1].value,Segment_Tree[Now<<1|1].value);
}

int Query_Tree(int Left,int Right,int Now,int Left_Edge,int Right_Edge) {
	int Query_Ans = 0;
	if(Left >= Left_Edge && Right <= Right_Edge) {
		return Segment_Tree[Now].value;
	}
	int Mid = (Left + Right) >> 1;
	if(Mid >= Left_Edge) {
		Query_Ans = max(Query_Ans,Query_Tree(Left,Mid,Now<<1,Left_Edge,Right_Edge));
	}
	if(Mid < Right_Edge) {
		Query_Ans = max(Query_Ans,Query_Tree(Mid+1,Right,Now<<1|1,Left_Edge,Right_Edge));
	}
	return Query_Ans;
}

void Deal_with() {
	int n,m;
	while(~scanf("%d %d",&n,&m)) {
		for(int i = 1 ; i <= n ; i++) {
			scanf("%d",a+i);
		}
		cnt = 1;
		Build_Tree(1,n,1);
		char tempc;
		int position,value;
		for(int i = 1 ; i <= m ; i++) {
			getchar();
			scanf("%c %d %d",&tempc,&position,&value);
			if(tempc == 'U') {
				Update_Tree(1,n,1,position,value);
			}
			else {
				printf("%d\n",Query_Tree(1,n,1,position,value));
			}
		}
	}
}

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