[HDOJ1754]I Hate It

题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=1754

线段树单点更新，查询最值。代码如下：

#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <algorithm>
#include <iostream>
#include <cmath>
#include <queue>
#include <map>
#include <stack>
#include <list>
#include <vector>

using namespace std;

const int maxn = 2000010;

typedef struct Node {
    int value;
    int left, right;
}Node;

Node node[maxn<<1];
int father[maxn];

inline int max(int a, int b) {
    return a > b ? a : b;
}

void build(int left, int right, int i) {
    node[i].left = left;
    node[i].right = right;
    node[i].value = 0;
    if(left == right) {
        father[left] = i;
        return ;
    }
    build(((left+right)>>1)+1, right, (i<<1)+1);
    build(left, (left+right)>>1, i<<1);
}

void update(int i) {
    if(i == 1) {    //根节点
        return ;
    }
    int fa = i / 2;
    int a = node[2*fa].value;   //左儿子
    int b = node[2*fa+1].value; //右儿子
    node[fa].value = max(a, b); //
    update(fa);
}

int ans;
void query(int left, int right, int i) {
    if(node[i].left == left && node[i].right == right){
        ans = max(ans, node[i].value);
        return ;
    }
    //left
    if(left <= node[2*i].right) {
        if(right <= node[2*i].right) {
            query(left, right, i<<1);
        }
        else {
            query(left, node[2*i].right, i<<1);
        }
    }
    //right
    if(right >= node[2*i+1].left) {
        if(left >= node[2*i+1].left) {
            query(left, right, (i<<1)+1);
        }
        else {
            query(node[2*i+1].left, right, (i<<1)+1);
        }
    }
}

int main() {
    // freopen("in", "r", stdin);
    int n, m;
    char cmd[2];
    int a, b, score;
    while(~scanf("%d %d", &n, &m)) {    
        build(1, n, 1);
        for(int i = 1; i <= n; i++) {
            scanf("%d", &score);
            node[father[i]].value = score;
            update(father[i]);
        }
        while(m--) {
            scanf("%s %d %d", cmd, &a, &b);
            if(cmd[0] == 'Q') {
                ans = 0;
                query(a, b, 1);
                printf("%d
", ans);
            }
            else if(cmd[0] == 'U') {
                node[father[a]].value = b;
                update(father[a]);
            }
        }
    }
    return 0;
}