HDU1754——I Hate It（线段树入门）

题目连接：I Hate It

思路：线段树基操
我被数组疯狂卡T，所以，要开大4倍的题目数组。。。

#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
using namespace std;
typedef long long ll;
#define MAXN 100005*8
#define INF 0x3f3f3f3f//将近int类型最大数的一半，而且乘2不会爆int
#define MOD 1000000007

int tree[MAXN];

void build(int l, int r, int node) {
	if (l == r) {
		scanf("%d", &tree[node]);
		return;
	}
	int mid = (l + r)>>1;
	build(l, mid, node<<1);
	build(mid+1, r, node<<1|1);
	tree[node] = max(tree[node<<1], tree[node<<1|1]);
}

void update(int p, int add, int l, int r, int node) {
	if (l == r) {
		tree[node] = add;		//根结点+add
		return;
	}
	int m = (l + r) >> 1;
	if (p <= m) update(p, add, l, m, node << 1);
	else update(p, add, m+1, r, node << 1 | 1);
	tree[node] = max(tree[node << 1], tree[node << 1 | 1]);
}

int query(int L, int R, int l, int r, int node) {
	if (L <= l && r <= R) return tree[node];
	int m = (l + r) >> 1, ret=0;
	if (L <= m) ret = max(ret, query(L, R, l, m, node << 1));
	if (R > m) ret = max(ret, query(L, R, m+1, r, node << 1 | 1));
	return ret;
}

int main()
{
	int n, m;
	while(~scanf("%d%d", &n, &m)){
		build(1, n, 1);
		for (int i = 0; i < m; ++i) {
			char ch[2];
			int a, b;
			scanf("%s%d %d", ch, &a, &b);
			if (ch[0] == 'U') update(a, b, 1, n, 1);
			else  printf("%d\n", query(a, b, 1, n, 1));
//            getchar();
		}
	}
	return 0;
}