技術標籤：線段樹acm競賽線段樹

題目連結： I Hate It

大致題意:

解題思路:

線段樹模板題，考察單點修改區間查詢，維護的是區間的最大值

AC程式碼:

#include <bits/stdc++.h>
using namespace std;
const int N = 2e5 + 10;
int n, m;
int w[N];
struct node {
	int l, r;
	int maxx;
}t[N * 4];

void pushup(int index) {
	t[index].maxx = max(t[index << 1].maxx,
 
 t[index << 1 | 1].maxx);
}
void build(int l, int r, int index = 1) {
	if (l == r)t[index] = { l,r,w[l] };
	else {
		t[index] = { l,r };
		int mid = l + r >> 1;
		build(l, mid, index << 1); build(mid + 1, r, index << 1 | 1);
		pushup(index);
	}
}
int ask(int l, int r, int index =
 
 1) {
	if (t[index].l >= l && t[index].r <= r)return t[index].maxx;
	else {
		int mid = t[index].l + t[index].r >> 1;
		int res = 0;
		if (l <= mid)res = ask(l, r, index << 1);
		if (r > mid)res = max(res, ask(l, r, index << 1 | 1));
		return res;
	}
}
void modify
 
(int x, int v, int index = 1) {
	if (t[index].l == x && t[index].r == x)t[index].maxx = v;
	else {
		int mid = t[index].l + t[index].r >> 1;
		if (x <= mid)modify(x, v, index << 1);
		if (x > mid)modify(x, v, index << 1 | 1);
		pushup(index);
	}
}
int main() {
	std::ios::sync_with_stdio(false);
	cin.tie(NULL);
	while (cin >> n >> m) {
		for (int i = 1; i <= n; ++i)cin >> w[i];
		build(1, n);
		while (m--) {
			char op[2]; int l, r;
			int x, v;
			cin >> op;
			if (*op == 'Q') {
				cin >> l >> r;
				cout << ask(l, r) << endl;
			}
			else {
				cin >> x >> v;
				modify(x, v);
			}
		}
	}
	return 0;
}

END