线段树——求区间最大最小值

//问最小值
//Q a b 询问(a,b)中最小值
//C a b 将a点值改为b
#include <bits/stdc++.h>
using namespace std;
#define maxn 200005

int min(int a, int b)
{
	return a>b ? b : a;
}
int tree[4 * maxn];

void pushup(int i)
{
	tree[i] = min(tree[i << 1], tree[i << 1 | 1]);
}

void build(int i, int l, int r)
{
	if (l == r)
	{
		scanf("%lld", &tree[i]);
		return;
	}
	int mid = (l + r) / 2;
	build(i << 1, l, mid);
	build(i << 1 | 1, mid + 1, r);
	pushup(i);
}

void update(int i, int l, int r, int x, int val)
{
	if (l == r)///l==x²»±ØÒª
	{
		tree[i] = val;
		return;
	}
	int mid = (l + r) / 2;
	if (x <= mid) update(i << 1, l, mid, x, val);
	else update(i << 1 | 1, mid + 1, r, x, val);
	pushup(i);
}

int query(int i, int l, int r, int x, int y)
{
	if (x <= l && r <= y)
		return tree[i];
	int minn = 9999999;
	int mid = (l + r) / 2;
	if (x <= mid) minn = min(minn, query(i << 1, l, mid, x, y));
	if (y>mid) minn = min(minn, query(i << 1 | 1, mid + 1, r, x, y));
	return minn;
}

int main()
{
	int n, m;
	int b, c;
	char a;
	while (scanf("%d%d", &n, &m) != -1)
	{
		build(1, 1, n);
		while (m--)
		{
			scanf(" %c%d%d", &a, &b, &c);
			if (a == 'Q')
				printf("%d\n", query(1, 1, n, b, c));
			else
				update(1, 1, n, b, c);
		}
	}
	return 0;
}

求区间最大值

#include <bits/stdc++.h>
using namespace std;
#define maxn 200005
int tree[4 * maxn];

void pushup(int i)
{
	tree[i] = max(tree[i << 1], tree[i << 1 | 1]);
}

void build(int i, int l, int r)
{
	if (l == r)
	{
		tree[i] = 0;
		return;
	}
	int mid = (l + r) / 2;
	build(i << 1, l, mid);
	build(i << 1 | 1, mid + 1, r);
	pushup(i);
}

void update(int i, int l, int r, int x, int val)
{
	if (l == r)
	{
		tree[i] = val;
		return;
	}
	int mid = (l + r) / 2;
	if (x <= mid) update(i << 1, l, mid, x, val);
	else update(i << 1 | 1, mid + 1, r, x, val);
	pushup(i);
}

int query(int i, int l, int r, int x, int y)
{
	if (x <= l && r <= y)
		return tree[i];
	int maxm = 0;
	int mid = (l + r) / 2;
	if (x <= mid) maxm = max(maxm, query(i << 1, l, mid, x, y));
	if (y>mid) maxm = max(maxm, query(i << 1 | 1, mid + 1, r, x, y));
	return maxm;
}

int main()
{
	int n, m;
	int b, c;
	char a;
	while (~scanf("%d%d", &n, &m))
	{
		build(1, 1, n);
		while (m--)
		{
			scanf(" %c%d%d", &a, &b, &c);
			if (a == 'Q')
				printf("%d\n", query(1, 1, n, b, c));
			else
				update(1, 1, n, b, c);
		}
	}
}