[线段树] [洛谷] P1531 I Hate It

线段树的区间查询和单点更新

复习敲一下

//#pragma GCC optimize(2)
#include <cstdio>
#include <iostream>
#include <cstdlib>
#include <cmath>
#include <cctype>
#include <string>
#include <cstring>
#include <algorithm>
#include <stack>
#include <queue>
#include <set>
#include <map>
#include <ctime>
#include <vector>
#include <fstream>
#include <list>
#include <iomanip>
#include <numeric>
using namespace std;
typedef long long ll;

const int MAXN = 1e6 + 10;

int arr[MAXN] ;

int tree[MAXN];

int N, M;

void init(int now, int l, int r)
{
    if(l == r)
    {
    	tree[now] = arr[l];
    	return ;
	}

    int mid = l + (r - l) / 2;

    init(now * 2, l, mid);
	
	init(now * 2 + 1, mid + 1, r);

    tree[now] = max(tree[now * 2], tree[now * 2 + 1]);

}

void change(int now, int l, int r, int find, int key)
{
	if(r < find || l > find)
		return ;
	if(l == r)
	{
		if(tree[now] < key)
			tree[now] = key;
		return ;
	}
	
	int mid = l + (r - l) / 2;
	
	change(now * 2, l, mid, find, key);
	
	change(now * 2 + 1, mid + 1, r, find, key);
	
	tree[now] = max(tree[now * 2], tree[now * 2 + 1]);
}

int qury(int now, int l, int r, int x, int y)
{
	if(l > y || r < x)
		return 0;
	if(x <= l && y >= r)
	{
		return tree[now];
	}
	
	int ans = 0;
	
	int mid = l + (r - l) / 2;
	
	ans = max(ans, qury(now * 2, l, mid, x, y) );
	
	ans = max(ans, qury(now * 2 + 1, mid + 1, r, x, y) );
	
	return ans;
}

int main()
{
    ios::sync_with_stdio(false);

    cin.tie(0);     cout.tie(0);

    cin>>N>>M;

    for(int i = 1; i <= N; i++)
        cin>>arr[i];

    init(1, 1, N);

    while(M--)
    {
    	char oprt;
    	
    	int x, y;
    	
    	cin>>oprt>>x>>y;
    	
    	if(oprt == 'Q')
    	{
    		cout<<qury(1, 1, N, x, y)<<endl;
    		
		}
    	
    	else
    	{
    		change(1, 1, N, x, y);
		}
	}

    return 0;
}