hdu 1754 I Hate It 解题报告 线段树

hdu 1754 I Hate It 解题报告 线段树

解题思路：线段树。线段树是树状数组的升级版，能进行区间查询，而树状数组只能使用前缀，但是树状数组编写简单。

#include<iostream>
#include<math.h>
#include<iomanip>
#include<algorithm>
#include<queue>
#include<cstring>
#include<string>
#include<string.h>
#include<map>
#include<stack>
#include<stdio.h>
#include<cstdio>
#include<stdlib.h>
#include<fstream>
#include<sstream>
#include<set>
#pragma warning(disable:4996)
#define INF 0x3f3f3f3f
#define ll long long
#define PI acos(-1.0)
const int N = 100005;
const int maxn = 1e9;
using namespace std;
int n, m;
int a[200005];
int tree[800020];//tree里放区间中的最大值
void build(int id, int l, int r)
{
	if (l == r)
	{
		tree[id] = a[l];
		return;
	}
	int mid = (l + r) >> 1;
	build(id << 1, l, mid);
	build(id << 1 | 1, mid + 1, r);
	tree[id] = max(tree[id << 1], tree[id << 1 | 1]);
}
int query(int id,int l,int r,int x,int y)
{
	if (x <= l && y >= r)
	{
		return tree[id];
	}
	int mid = (l + r) >> 1;
	int mx = -1 << 30;//初始为负无穷
	if (x <= mid)
		mx = max(mx, query(id << 1, l, mid, x, y));
	if (y > mid)
		mx = max(mx, query(id << 1 | 1, mid + 1, r, x, y));
	return mx;
}
void update(int id, int l, int r, int x, int y)
{
	if (l == r)
	{
		tree[id] = y;
		return;
	}
	int mid = (l + r) >> 1;
	if (x <= mid)
		update(id << 1, l, mid, x, y);
	else
		update(id << 1 | 1, mid + 1, r, x, y);
	tree[id] = max(tree[id << 1], tree[id << 1 | 1]);
}
int main()
{
	while (scanf("%d%d",&n,&m)!=EOF)
	{
		memset(a, 0, sizeof(a));
		for (int i = 1; i <= n; i++)
		{
			scanf("%d", &a[i]);
		}
		build(1, 1, n);
		while (m--)
		{
			char ch;
			int x, y;
			scanf(" %c%d%d", &ch, &x, &y);//注意%c前面要留空格将上一行键入的回车消除
			if (ch == 'Q')
				printf("%d\n", query(1, 1, n, x, y));
			else
				update(1, 1, n, x, y);
		}
	}
}