关于以下两种tarjan写法

bool ins[MAXN];//是否在栈内
inline void tarjan( int x ){
	dfn[x] = low[x] = ++_time;
	s[++top] = x;
	ins[x] = 1;
	for( int i = head[x]; i; i = e[i].nxt ){
		int y = e[i].v;
		if( !dfn[y] ){
			tarjan( y );
			low[x] = min( low[x], low[y] );
		}
		else if( ins[y] ) low[x] = min( low[x], dfn[y] );
	}
	if( dfn[x] == low[x] ){
		int y = inf;
		tot++;
		while( x != y ){
			y = s[top--];
			ins[y] = 0;
			belong[y] = tot;
			dis[tot] += val[y];
		}
	}
}

int belong[MAXN], tot;//SCC编号，总数
inline void tarjan( int x ){
	dfn[x] = low[x] = ++_time;
	s[++top] = x;
	for( int i = head[x]; i; i = e[i].nxt ){
		int y = e[i].v;
		if( !dfn[y] ){
			tarjan( y );
			low[x] = min( low[x], low[y] );
		}
		else if( !belong[y] ) low[x] = min( low[x], dfn[y] );
	}
	if( dfn[x] == low[x] ){
		int y = inf;
		tot++;
		while( x != y ){
			y = s[top--];
			belong[y] = tot;
			dis[tot] += val[y];
		}
	}
}

其中

else if( !belong[y] ) low[x] = min( low[x], dfn[y] );

和 else if( ins[y] ) low[x] = min( low[x], dfn[y] ); 都可以AC，请问这两种写法有什么区别呢?