hdu 1754 I Hate It (线段树)

中规中矩，单点更新，区间求最值。

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <string.h>
#include <time.h>
#include <algorithm>

using namespace std;

const int N = 200005;

int num[N << 2];

void Update(int i){
    num[i] = max(num[i * 2], num[i * 2 + 1]); 　　　　//更新父亲节点
}

void Build(int left, int right, int i){　　　　//建树
    if(left == right){
        scanf("%d%", &num[i]);
        return;
    }
    int mid = (left + right) / 2;
    Build(left, mid, i * 2);
    Build(mid + 1, right, i * 2 + 1);
    Update(i);
}

void Change(int loc, int number, int left, int right, int i){　　　　//单点更新
    if(left == right){
        num[i] = number;
        return;
    }
    int mid = (left + right) / 2;
    if(loc <= mid) Change(loc, number, left, mid, i * 2);
    else Change(loc, number, mid + 1, right, i * 2 + 1);
    Update(i);
}

int Query(int ll, int rr, int left, int right, int i){　　　　//区间求最值
    if(ll == left && rr == right) return num[i];
    int mid = (left + right) / 2;
    if(rr <= mid) return Query(ll, rr, left, mid, i * 2);
    else if(ll > mid) return Query(ll, rr, mid + 1, right, i * 2 + 1);
    else return max(Query(ll, mid, left, mid, i * 2), Query(mid + 1, rr, mid + 1, right, i * 2 + 1));
}

int main(){
    int N, M;
    while(~scanf("%d%d", &N, &M)){
        Build(1, N, 1);
        while(M--){
            char order[2];
            int a, b;
            scanf("%s%d%d", order, &a, &b);
            if(order[0] == ‘Q‘) printf("%d\n", Query(a, b, 1, N, 1));
            else if(order[0] == ‘U‘) Change(a, b, 1, N, 1);
        }
    }
}