线段树的应用

维护最大值

之前知道cin cout 会比scanf慢
但是没有遇到一道题是真正因为cin cout TLE的
这题是第一个 不用scanf就会TLE

#include<bits/stdc++.h>
using namespace std;
const int N = 1e5 + 10;
int n, m;
struct tr {
    int l, r, maxv;
    tr() {
        l = 0;
        r = 0;
        maxv = 0;
    }
    tr(int a, int b, int c) {
        l = a; r = b; maxv = c;
    }

}tre[4 * N];
int w[N];
int pushup(int u) {
    tre[u].maxv = max(tre[u << 1].maxv, tre[u << 1 | 1].maxv);
}
void build(int u, int l, int r) {
    if (l == r)
    {
        tre[u] = tr(l, r, w[r]);
    }
    else {
        tre[u] = tr(l, r, 0);
        int mid = l + r >> 1;
        build(u << 1, l, mid);
        build(u << 1 | 1, mid + 1, r);
        pushup(u);
        //tre[u].maxv = max(tre[u << 1].maxv, tre[u << 1 | 1].maxv);

    }
}
int query(int u, int l, int r) {
    if (tre[u].l >= l && tre[u].r <= r)
        return tre[u].maxv;
    int mid = tre[u].l + tre[u].r >> 1;
    int maxv = -2e9;
    if (l <= mid)
        maxv = query(u << 1, l, r);
    if (r >= mid + 1)
        maxv = max(maxv, query(u << 1 | 1, l, r));
    return maxv;
}
int main()
{
//  ios::sync_with_stdio(false);
    //cin.tie(0);cout.tie(0);
    //cin >> n >> m;
    scanf("%d%d", &n, &m);
    for (int i = 1; i <= n; i++)
        //cin>>w[i];
        scanf("%d", &w[i]);
    int l, r;
    build(1, 1, n);
    while (m--) {
        //cin>>l>>r;
        scanf("%d%d", &l, &r);
            //cout << query(1, l, r) << endl;
        printf("%d\n", query(1, l, r));

    }

    return 0;
}