刚开始学线段树

求助大佬们

题面

#include<iostream>
using namespace std;
int n, q;
int a[50010];
struct tree {
	int mn, mx;
}tr[200010];
void build(int rt, int l, int r) {
	if(l == r) {
		tr[rt].mx = a[l];
		tr[rt].mn = a[l];
		return;
	}
	int mid = (l + r) >> 1;
	build(rt << 1, l, mid);
	build(rt << 1 | 1, mid + 1, r);
	tr[rt].mn = min(tr[rt << 1].mn, tr[rt << 1 | 1].mn);
	tr[rt].mx = max(tr[rt << 1].mx, tr[rt << 1 | 1].mx);
}
int calc_mx(int rt, int l, int r, int x, int y) {
	if(l == x && r == y) return tr[rt].mx;
	int mid = (l + r) >> 1;
	if(y <= mid) return calc_mx(rt << 1, l, mid, x, y);
	else if(x > mid) return calc_mx(rt << 1 | 1, mid + 1, r, x, y);
	else return max(calc_mx(rt << 1, l, mid, x, mid), calc_mx(rt << 1 | 1, mid + 1, r, mid + 1, y));
}
int calc_mn(int rt, int l, int r, int x, int y) {
	if(l == x && r == y) return tr[rt].mn;
	int mid = (l + r) >> 1;
	if(y <= mid) return calc_mn(rt << 1, l, mid, x, y);
	else if(x > mid) return calc_mn(rt << 1 | 1, mid + 1, r, x, y);
	else return min(calc_mn(rt << 1, l, mid, x, mid), calc_mn(rt << 1 | 1, mid + 1, r, mid + 1, y));
}
int main() {
	cin >> n >> q;
	for(int i = 1; i <= n; i ++) scanf("%d", &a[i]);
	build(1, 1, n);
	for(int i = 1; i <= 4 * n; i ++) printf("%d ", tr[i].mx);
	for(int i = 1; i <= q; i ++) {
		int x, y;
		scanf("%d", &x, &y);
		printf("%d\n", calc_mx(1, 1, n, x, y) - calc_mn(1, 1, n, x, y));
	}
	return 0;
}