HDU 1754 I hate it 分段树Segment Tree题解

给出一段数据，然后要更新单个数据，会询问一段数据中的最大值。

又是一道分段树操作。渐渐熟手了。

#pragma once
#include <cstdio>
#include <algorithm>
using namespace std;

class IHateIt_1754_1
{
	static const int SIZE = 200001;
	int *segTree;	//不要使用segTree[SIZE<<2]

	inline int lChild(int r) { return r<<1; }
	inline int rChild(int r) { return r<<1|1; }

	void pushUp(int rt)
	{
		segTree[rt] = max(segTree[lChild(rt)], segTree[rChild(rt)]);
	}

	void build(int l, int r, int rt)
	{
		if (l == r)
		{
			scanf("%d", &segTree[rt]);
			return ;
		}
		int m = l + ((r-l)>>1);
		build(l, m, lChild(rt));
		build(m+1, r, rChild(rt));
		pushUp(rt);
	}

	void update(const int stu, const int score, int l, int r, int rt)
	{
		if (l == r)
		{
			segTree[rt] = score;
			return ;
		}

		int m = l + ((r-l)>>1);
		if (stu <= m) update(stu, score, l, m, lChild(rt));
		else update(stu, score, m+1, r, rChild(rt));
		pushUp(rt);
	}

	int query(const int L, const int R, int l, int r, int rt)
	{
		if (L <= l && r <= R) return segTree[rt];

		int m = l + ((r-l)>>1);
		int res = 0;

		if (L <= m) res = query(L, R, l, m, lChild(rt));//注意下标
		if (R > m) res = max(res, query(L, R, m+1, r, rChild(rt)));
		return res;
	}
public:
	IHateIt_1754_1() : segTree((int *) malloc (sizeof(int) * (SIZE<<2)))
	{
		int N, M;
		while (scanf("%d %d", &N, &M) != EOF)
		{
			build(1, N, 1);
			while (M--)
			{
				char op[2];
				int a, b;
				scanf("%s%d%d", op, &a, &b);
				if (op[0] == 'U') update(a, b, 1, N, 1);
				else printf("%d\n",query(a, b, 1, N, 1));
			}
		}
	}
	~IHateIt_1754_1()
	{
		if (segTree) free(segTree);
	}
};

HDU 1754 I hate it 分段树Segment Tree题解