写一个线段树，用C++

以下是一个简单的线段树实现，包含区间修改和查询最大值的功能。

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define MAXN 100005

int n, m;
int a[MAXN];
int tree[MAXN << 2];

void build(int k, int l, int r) {
    if (l == r) {
        tree[k] = a[l];
        return;
    }
    int m = (l + r) >> 1;
    build(k << 1, l, m);
    build(k << 1 | 1, m + 1, r);
    tree[k] = tree[k << 1] > tree[k << 1 | 1] ? tree[k << 1] : tree[k << 1 | 1];
}

void update(int k, int l, int r, int x, int v) {
    if (l == r) {
        tree[k] = v;
        return;
    }
    int m = (l + r) >> 1;
    if (x <= m) {
        update(k << 1, l, m, x, v);
    } else {
        update(k << 1 | 1, m + 1, r, x, v);
    }
    tree[k] = tree[k << 1] > tree[k << 1 | 1] ? tree[k << 1] : tree[k << 1 | 1];
}

int query(int k, int l, int r, int x, int y) {
    if (x <= l && r <= y) {
        return tree[k];
    }
    int m = (l + r) >> 1, ret = 0;
    if (x <= m) {
        ret = query(k << 1, l, m, x, y);
    }
    if (y > m) {
        int t = query(k << 1 | 1, m + 1, r, x, y);
        if (t > ret) {
            ret = t;
        }
    }
    return ret;
}

int main() {
    scanf("%d %d", &n, &m);
    for (int i = 1; i <= n; i++) {
        scanf("%d", &a[i]);
    }
    build(1, 1, n);
    while (m--) {
        int op, x, y;
        scanf("%d %d %d", &op, &x, &y);
        if (op == 1) {
            update(1, 1, n, x, y);
        } else {
            printf("%d\n", query(1, 1, n, x, y));
        }
    }
    return 0;
}