HDU 1754 I Hate It（线段树，最值查询）

HDU 1754 I Hate It（线段树，最值查询）

ACM

题目地址：HDU 1754 I Hate It

题意： 
中文题，不解释。

分析： 
裸的单点更新求区间最值。

代码：

/*
*  Author:      illuz <iilluzen[at]gmail.com>
*  Blog:        http://blog.youkuaiyun.com/hcbbt
*  File:        1754.cpp
*  Create Date: 2014-08-05 09:46:17
*  Descripton:  segment tree 
*/

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
#define repf(i,a,b) for(int i=(a);i<=(b);i++)

#define lson(x) ((x) << 1)
#define rson(x) ((x) << 1 | 1)

typedef long long ll;

const int N = 200100;
const int ROOT = 1;

// below is sement point updated
struct seg {
    ll w;
};

struct segment_tree { 
    seg node[N << 2];

    void update(int pos) {
        node[pos].w = max(node[lson(pos)].w, node[rson(pos)].w);
    }

    void build(int l, int r, int pos) {
        if (l == r) {
            scanf("%lld", &node[pos].w);
            return;
        }
        int m = (l + r) >> 1;
        build(l, m, lson(pos));
        build(m + 1, r, rson(pos));
        update(pos);
    }

    void modify(int l, int r, int pos, int x, ll y) {
        if (l == r) {
            node[pos].w = y;
            return;
        }
        int m = (l + r) >> 1;
        if (x <= m)
            modify(l, m, lson(pos), x, y);
        else
            modify(m + 1, r, rson(pos), x, y);
        update(pos);
    }

    // query the segment [x, y]
    ll query(int l, int r, int pos, int x, int y) {
        if (x <= l && r <= y)
            return node[pos].w;
        int m = (l + r) >> 1;
        ll res = 0;
        if (x <= m)
            res = max(res, query(l, m, lson(pos), x, y));
        if (y > m)
            res = max(res, query(m + 1, r, rson(pos), x, y));
        return res;
    }
} sgm;

int n, m, a, b;
char op[3];

int main() {
    while (~scanf("%d%d", &n, &m)) {
        sgm.build(1, n, ROOT);
        while (m--) {
            scanf("%s%d%d", op, &a, &b);
            if (op[0] == 'U') {
                sgm.modify(1, n, ROOT, a, b);
            } else {
                printf("%d\n", sgm.query(1, n, ROOT, a, b));
            }
        }
    }
    return 0;
}