HDU-1754 I Hate It 线段树-优快云博客

本文介绍了一种基于段式树的数据结构实现方法，通过构建、更新和查询操作，高效地处理数组中最大值的查询任务。代码示例展示了如何初始化段式树，更新特定位置的数值，并查询指定区间内的最大值。

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#include "stdio.h"
#include "string.h"
#include "algorithm"
using namespace std;
const int maxn = 200005;
const int inf = 1<<30;
int n,m;
int x,y,ad,ans;
int tree[maxn*3];
int c[maxn];
void PushUp( int t )
{
	tree[t]= tree[t<<1] >= tree[t<<1|1]?tree[t<<1] : tree[t<<1|1];
}
void buildtree( int ld,int rd,int t )
{
	if( ld == rd )
	{
		tree[t] = c[ld];
		return;
	}
	int mid = ( ld + rd )>>1;
	buildtree( ld,mid,t<<1 );
	buildtree( mid+1,rd,t<<1|1 );
	PushUp(t);
}
void updata( int ld,int rd,int t )
{
	if( ld == rd )
	{
		tree[t] = ad;
		return;
	}
	int mid = ( ld + rd )>>1;
	if( x <= mid )  
		updata( ld,mid,t<<1 );
	else if( x > mid )   
		updata( mid+1,rd,t<<1|1 );
	PushUp(t);
}
void query( int ld,int rd,int t )
{
	if( ld >= x && rd <= y )
	{
		ans = ans > tree[t]?ans : tree[t];
		return;
	}
	int mid = ( ld + rd )>>1;
	if( x <= mid )
		query( ld,mid,t<<1 );
	if( y > mid )
		query( mid+1,rd,t<<1|1 );
}
int main()
{
	//freopen( "data.txt","r",stdin );
	char ch[3];
	while( scanf("%d%d",&n,&m) == 2 )
	{
		for( int i = 1; i <= n; i ++ )
		{
			scanf("%d",&c[i]);
		}
		buildtree(1,n,1);	
		for( int i = 1; i <= m; i ++ )
		{
			getchar();
			scanf("%s",ch);
			if( ch[0] == 'Q' )
			{
				scanf("%d%d",&x,&y);
				ans = -inf;
				query( 1,n,1 );
				printf("%d\n",ans);
			}
			else if( ch[0] == 'U' )
			{
				scanf("%d%d",&x,&ad);
				updata( 1,n,1 );
			}
		}
	}
    return 0;
}