HDU-1754

链接：https://vjudge.net/problem/HDU-1754

思路：

线段树模板题

代码：

//#include <bits/stdc++.h>
#include <iostream>
#include <algorithm>
#include <math.h>
#include <string>
using namespace std;
const int MAXN = 2e6+10;
struct Node
{
    int value;//线段树中每个位置对应的最大值
    int left,right;//位置对应的区间
}node[MAXN*2];
int Father[MAXN];
int Max;

void BuildTree(int i,int left,int right)
{
    //构建线段树
    node[i].left = left;
    node[i].right = right;
    node[i].value = 0;
    if (left == right)
    {
        Father[left] = i;//原数组位置对应在线段树中的结点
        return;
    }
    BuildTree(i<<1,left,(int)(floor(left+right)/2.0));//构建左子树
    BuildTree((i<<1)+1,(int)(floor(left+right)/2.0)+1,right);//构建右子树
}

void UpdateTree(int ri)
{
    if (ri == 1)
        return ;
    int fi = ri/2;
    int a = node[fi<<1].value;
    int b = node[(fi<<1)+1].value;//当前结点和其兄弟结点
    node[fi].value = max(a,b);//当前结点的父节点的最大值
    UpdateTree(fi);
}

void Query(int i,int left,int right)
{
    //查询区间最大值
    if (node[i].left == left&&node[i].right == right)
    {
        Max = max(Max,node[i].value);
        return;
    }
    i <<= 1;
    if (left <= node[i].right)//查询区间交叉
    {
        if (right <= node[i].right)//查询区间完全属于左结点
            Query(i,left,right);
        else
            Query(i,left,node[i].right);//查询区间部分属于左节点
    }
    i++;
    if (right >= node[i].left)
    {
        if (left >= node[i].left)//查询区间完全属于右结点
            Query(i,left,right);
        else
            Query(i,node[i].left,right);//查询区间部分属于右结点
    }
}

int main()
{
    int n,m,g;
    ios::sync_with_stdio(false);

    //while (cin >> n >> m)
    while (~scanf("%d%d",&n,&m))
    {
        BuildTree(1,1,n);
        for (int i = 1;i<=n;i++)
        {
            scanf("%d",&g);
            node[Father[i]].value = g;//给只包含一个位置的结点更新值
            UpdateTree(Father[i]);//初始化所有父节点
        }
        char op[10];
        int l,r;
        for (int i = 1;i<=m;i++)
        {
            //cin >> op >> l >> r;
            scanf("%s%d%d",op,&l,&r);
            if (op[0] == 'Q')
            {
                Max = 0;
                Query(1,l,r);
                cout << Max << endl;
            }
            else
            {
                node[Father[l]].value = r;//更新单个结点值
                UpdateTree(Father[l]);//更新更改结点所有父节点
            }
        }
    }

    return 0;
}