bzoj2843

lct 水水水

#include <cstdio>

int ch[30010][2],fa[30010],lz[30010],x[30010],sum[30010];

int n,m;

int st[30010],tp;

int read_int () {
	char c = getchar();
	int re = 0;
	for(;c > '9' || c < '0'; c = getchar());
	for(;c >= '0' && c <= '9';c = getchar())
		re = re * 10 + c - '0';
	return re;
}

void reverse (int u) {
	int t = ch[u][0];
	ch[u][0] = ch[u][1];
	ch[u][1] = t;
	lz[u] ^= 1;
}

void pd (int u) {
	if(!lz[u])
		return;
	lz[u] = 0;
	reverse(ch[u][0]);
	reverse(ch[u][1]);
}

void pu (int u) {
	sum[u] = x[u] + sum[ch[u][0]] + sum[ch[u][1]];
}

void rot (int u,int d) {
	ch[fa[u]][d ^ 1] = ch[u][d];
	if(ch[u][d])
		fa[ch[u][d]] = fa[u];
	ch[u][d] = fa[u];
	int t = fa[ch[u][d]];
	fa[ch[u][d]] = u;
	fa[u] = t;
	
	pu(ch[u][d]);
	pu(u);
	
	if(!t)
		return;
	if(ch[t][0] == ch[u][d])
		ch[t][0] = u;
	if(ch[t][1] == ch[u][d])
		ch[t][1] = u;
}

void splay (int u) {
	int t = u;
	st[tp = 1] = t;
	while(ch[fa[t]][0] == t || ch[fa[t]][1] == t) {
		t = fa[t];
		st[++tp] = t;
	}
	while(tp) {
		pd(st[tp]);
		--tp;
	}
	
	while(ch[fa[u]][0] == u || ch[fa[u]][1] == u) {
		if(ch[fa[fa[u]]][0] != fa[u] && ch[fa[fa[u]]][1] != fa[u]) {
			if(ch[fa[u]][0] == u)
				rot(u,1);
			else rot(u,0);
		}
		else {
			int d = ch[fa[fa[u]]][0] == fa[u];
			if(ch[fa[u]][d] == u) {
				rot(u,d ^ 1);
				rot(u,d);
			}
			else {
				rot(u,d);
				rot(u,d);
			}
		}
	}
}

void access (int u) {
	int v = 0;
	while(u) {
		splay(u);
		ch[u][1] = v;
		
		pu(u);
		
		v = u;
		u = fa[u];
	}
}

void mtr (int u) {
	access(u);
	splay(u);
	reverse(u);
}

int fr (int u) {
	access(u);
	splay(u);
	int t = u;
	while(ch[t][0])
		t = ch[t][0];
	return t;
}

int main () {
	
	n = read_int();
	for(int i = 1;i <= n;++i)
		x[i] = read_int();
	m = read_int();
	
	char C;
	int u,v;
	for(int i = 1;i <= m;++i) {
		scanf(" %c",&C);
		u = read_int();
		v = read_int();
		if(C == 'b') {
			if(fr(u) == fr(v))
				printf("no\n");
			else {
				printf("yes\n");
				mtr(u);
				mtr(v);
				fa[u] = v;
			}
		}
		else {
			if(C == 'p') {
				splay(u);
				x[u] = v;
				pu(u);
			}
			else {
				if(fr(u) != fr(v))
					printf("impossible\n");
				else {
					mtr(u);
					access(v);
					splay(v);
					printf("%d\n",sum[v]);
				}
			}
		}
	}
}