线段树 单点修改 区间求最大

#include <stdio.h>
#define sc(x) scanf("%lld", &(x))
#define pr(x) printf("%lld\n", (x))
#define max(a, b) ((a) > (b) ? (a) : (b))
#define int ll
typedef long long ll;
const int N = 2e5 + 7;
const ll mod = 1e9 + 7;
int a[N], tree[N << 2], n;
void bulid(int p = 1, int l = 1, int r = n) {
    if (l == r) {
        tree[p] = a[l];
        return;
    }
    int mid = (l + r) / 2;
    bulid(p * 2, l, mid);
    bulid(p * 2 + 1, mid + 1, r);
    tree[p] = max(tree[p * 2], tree[p * 2 + 1]);
}
void upd(int p, int l, int r, int x, int num) {
    if (l == r) {
        if (l == x) tree[p] = num;
        return;
    }
    int mid = (l + r) / 2;
    if (x <= mid)
        upd(p * 2, l, mid, x, num);
    else
        upd(p * 2 + 1, mid + 1, r, x, num);
    tree[p] = max(tree[p * 2], tree[p * 2 + 1]);
}
int query(int p, int l, int r, int x, int y) {
    if (x <= l && r <= y) return tree[p];
    int mid = (l + r) / 2;
    if (y <= mid) return query(p * 2, l, mid, x, y);
    if (x > mid) return query(p * 2 + 1, mid + 1, r, x, y);
    int La = query(p * 2, l, mid, x, mid),
        Ra = query(p * 2 + 1, mid + 1, r, mid + 1, y);
    return max(La, Ra);
}
signed main() {
    int m, x, y;
    char op;
    while (~sc(n) && ~sc(m)) {
        for (int i = 1; i <= n; ++i) sc(a[i]);
        bulid();
        while (m--) {
            getchar(), op = getchar();
            sc(x), sc(y);
            if (op == 'Q')
                pr(query(1, 1, n, x, y));
            else
                upd(1, 1, n, x, y);
        }
    }
    return 0;
}