单点修改，区间维护最小值的线段树。

#include <cstdio>
#include <algorithm>
using namespace std;
struct node {
	int l, r, lc, rc, minn;
}tr[400005];
int a[200005];
int build(int l, int r) {
	static int cnt = 0;
	int pos = ++cnt;
	tr[pos].l = l;
	tr[pos].r = r;
	if (l == r) {
		tr[pos].lc = tr[pos].rc = -1;
		tr[pos].minn = a[l];
	} else {
		tr[pos].lc = build(l, l + r >> 1);
		tr[pos].rc = build((l + r >> 1) + 1, r);
		tr[pos].minn = min(tr[tr[pos].lc].minn, tr[tr[pos].rc].minn);
	}
	return pos;
}
void change(int pos, int x, int y) {
	if (tr[pos].l == tr[pos].r) {
		tr[pos].minn = y;
		return;
	}
	if (x <= tr[tr[pos].lc].r)
		change(tr[pos].lc, x, y);
	else
		change(tr[pos].rc, x, y);
	tr[pos].minn = min(tr[tr[pos].lc].minn, tr[tr[pos].rc].minn);
}
int query(int pos, int l, int r) {
	if (tr[pos].l == l && tr[pos].r == r)
		return tr[pos].minn;
	if (r <= tr[tr[pos].lc].r)
		return query(tr[pos].lc, l, r);
	if (l >= tr[tr[pos].rc].l)
		return query(tr[pos].rc, l, r);
	return min(query(tr[pos].lc, l, tr[tr[pos].lc].r), query(tr[pos].rc, tr[tr[pos].rc].l, r));
}
int main() {
	int n, m;
	scanf("%d%d", &n, &m);
	for (int i = 1; i <= n; i++)
		scanf("%d", &a[i]);
	build(1, n);
	while (m--) {
		char c[2];
		int a, b;
		scanf("%s%d%d", c, &a, &b);
		if (c[0] == 'Q') {
			if (a > b)
				swap(a, b);
			printf("%d\n", query(1, a, b));
		}
		else
			change(1, a, b);
	}
	return 0;
}