hdu 1754 简单的线段树应用

本来想找些树状数组的题做做，看到这题，不知道用树状数组的话应该如何做，就还是用线段树了。

/*
 * hdu1754/win.cpp
 * Created on: 2011-9-6
 * Author    : ben
 */
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <algorithm>
using namespace std;

const int MAXN = 200100;
const int MAX_NODE = 400100;
int N, M, nCount;
int scores[MAXN];

typedef struct CNode {
    int L, R;
    int maxscore;
    CNode *pLeft, *pRight;
} CNode;

CNode Tree[MAX_NODE];

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

//建立线段树
void BuildTree(CNode *pRoot, int L, int R) {
    pRoot->L = L;
    pRoot->R = R;
    if (L == R) {
        pRoot->maxscore = scores[L];
        return;
    }
    nCount++;
    pRoot->pLeft = Tree + nCount;
    nCount++;
    pRoot->pRight = Tree + nCount;
    int mid = (L + R) / 2;
    BuildTree(pRoot->pLeft, L, mid);
    BuildTree(pRoot->pRight, mid + 1, R);
    pRoot->maxscore = mymax(pRoot->pLeft->maxscore, pRoot->pRight->maxscore);
}

//插入数据
void Update(CNode *pRoot, int index) {
    if (pRoot->L == pRoot->R) {
        pRoot->maxscore = scores[index];
        return;
    }
    int mid = (pRoot->L + pRoot->R) / 2;
    if (index <= mid) {
        Update(pRoot->pLeft, index);
    } else {
        Update(pRoot->pRight, index);
    }
    pRoot->maxscore = mymax(pRoot->pLeft->maxscore, pRoot->pRight->maxscore);
}

int Query(CNode *pRoot, int from, int to) {
    if (pRoot->L == from && pRoot->R == to) {
        return pRoot->maxscore;
    }
    int mid = (pRoot->L + pRoot->R) / 2;
    if (mid >= from && mid < to) {
        int m1, m2;
        m1 = Query(pRoot->pLeft, from, mid);
        m2 = Query(pRoot->pRight, mid + 1, to);
        return mymax(m1, m2);
    } else if (mid >= to) {
        return Query(pRoot->pLeft, from, to);
    } else {
        return Query(pRoot->pRight, from, to);
    }
}

void work();
int main() {
#ifndef ONLINE_JUDGE
    freopen("data.in", "r", stdin);
#endif
    work();
    return 0;
}

void work() {
    char op;
    int a, b;
    while (scanf("%d%d", &N, &M) == 2) {
        for (int i = 1; i <= N; i++) {
            scanf("%d", &scores[i]);
        }
        nCount = 0;
        BuildTree(Tree, 1, N);
        for (int i = 0; i < M; i++) {
            scanf(" %c", &op);
            if (op == 'Q') {
                scanf("%d%d", &a, &b);
                printf("%d\n", Query(Tree, a, b));
            } else {
                scanf("%d%d", &a, &b);
                scores[a] = b;
                Update(Tree, a);
            }
        }
    }
}