线段树(单点更新，区间查询) HDU 1754 I Hate It

题目链接

线段树的模板

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

using namespace std;

const int Maxn = 2e6 + 10;
int fa[Maxn];
struct node
{
    int l, r;
    int value;
    int mid() {
        return (l + r) / 2;
    }
}s[Maxn];
void build(int i, int l, int r)
{
    s[i].l = l;
    s[i].r = r;
    s[i].value = 0;
    while (r == l) {
        fa[l] = i;
        return;
    }
    build(i * 2, l, (l + r) / 2);
    build(i * 2 + 1, (l + r) / 2 + 1, r);
}
void updata(int x)
{
    if (x == 1) return;
    int fi = x / 2;
    int a = s[fi * 2].value;
    int b = s[fi * 2 + 1].value;
    s[fi].value = max(a, b);
    updata(fi);
}
int Max;
void query(int i, int l, int r)
{
    if (s[i].l == l && s[i].r == r) {
        Max = max(Max, s[i].value);
        return;
    }
    int m = s[i].mid();
    if (r <= m) query(i << 1, l, r);
    else if (l > m) query(i << 1 | 1, l, r);
    else {
        query(i << 1, l, m);
        query(i << 1 | 1, m + 1, r);
    }
    
}
int main()
{
    int n, m;
    while (scanf("%d %d", &n, &m) == 2) {
        build(1, 1, n);
        for (int i = 1;i <= n;i++) {
            int x;
            scanf("%d", &x);
            s[fa[i]].value = x;
            updata(fa[i]);
        }
        while (m--) {
            char t[10];
            int a, b;
            scanf("%s", t);
            scanf("%d %d", &a, &b);
            if (t[0] == 'Q') {
                Max = 0;
                query(1, a, b);
                printf("%d
", Max);
            }
            else {
                s[fa[a]].value = b;
                updata(fa[a]);
            }
        }
    }
    return 0;
}