hdu 1754 线段树单点修改＋区间查询_zkw线段树单点查询区间修改-优快云博客

本文链接：https://blog.youkuaiyun.com/qq_24451605/article/details/44017699

本文介绍了一种使用线段树进行区间查询与更新的经典算法实现。通过递归构建、更新和查询线段树节点，可以高效地解决一系列区间操作问题。适用于需要快速查询区间最大值并能动态修改区间元素的场景。

摘要生成于 C知道，由 DeepSeek-R1 满血版支持，前往体验 >

#include <iostream>
#include <cstring>
#include <cstdio>
#include <algorithm>
#define MAX 200007
#define INF 10000000

using namespace std;

int n,m;
int a[MAX];

struct Node
{
    int l,r,maxn;
}tree[MAX<<2];

void push_up ( int u )
{
    tree[u].maxn = max ( tree[u<<1].maxn , tree[u<<1|1].maxn );
}

void build ( int u , int l  , int r )
{
    tree[u].l = l , tree[u].r = r;
    if ( l == r )
    {
        tree[u].maxn = a[l];
        return;
    }
    int mid = l + r >> 1;
    build ( u<<1 , l , mid );
    build ( u<<1|1 , mid+1 , r );
    push_up ( u );
}

void update ( int u , int x , int v )
{
    int l = tree[u].l , r = tree[u].r;
    if ( l == r )
    {
        tree[u].maxn = v;
        return;
    }
    int mid = l+r>>1;
    if ( x > mid ) update ( u<<1|1 , x , v );
    else update ( u<<1 , x , v );
    push_up ( u );
}

int query ( int u , int left , int right )
{
    int l = tree[u].l , r = tree[u].r;
    if ( left <= l && r <= right )
        return tree[u].maxn;
    int mid = l + r >> 1;
    int ret = -INF;
    if ( right >= l && left <= mid )
       ret = max ( ret , query ( u<<1 , left , right ) );
    if ( right > mid && left <= r ) 
       ret = max ( ret , query ( u<<1|1 , left , right ) );
    return ret; 
}

int main ( )
{
    while ( ~scanf ( "%d%d" , &n , &m ) )
    {
        for ( int i = 1 ; i <= n ; i++ )
            scanf ( "%d" , &a[i] );
        build ( 1 , 1 , n );
        char s[5];
        int l , r;
        for ( int i = 0 ; i < m ; i++ )
        {
            scanf ( "%s" , s );
            scanf ( "%d%d" , &l , &r );
            if ( s[0] == 'Q' )
                printf ( "%d\n" , query ( 1 , l , r ) );
            else update ( 1 , l , r );
        }
    }
}