哪里不对orz了

#include<bits/stdc++.h>
using namespace std;
bool vis[1000][1000];
int x,y,z;
struct node{
	int a,b,steps;
};
queue<node>q;		
int main()
{
	cin>>x>>y>>z;
	node no;
	no.a=0;no.b=0;no.steps=0;
	q.push(no);
	vis[0][0]=1;
	while(!q.empty())
	{	
		node u=q.front();
		q.pop();
		int a=u.a,b=u.b,t=u.steps;
		if(a==z||b==z)
		{
			cout<<t<<endl;
			return 0;
		}
		
		if(a!=x&&!vis[x][b])q.push((node){x,b,t+1}),vis[x][b]=1;
		if(b!=y&&!vis[a][y])q.push((node){a,y,t+1}),vis[a][y]=1;
		if(!a&&!vis[0][b])q.push((node){0,b,t+1}),vis[0][b]=1;
		if(!b&&!vis[a][0])q.push((node){a,0,t+1}),vis[a][0]=1;
		if(a)
		{
			if(y-b>=a&&!vis[0][a+b])
				q.push((node){0,b+a,t+1}),vis[0][a+b]=1;
			else if(y-b<a&&!vis[a-(y-b)][y])
				q.push((node){a+b-y,y,t+1}),vis[a+b-y][y]=1;
		}
		if(b)
		{
			if(x-a>=b&&!vis[a+b][0])
				q.push((node){a+b,0,t+1}),vis[a+b][0]=1;
			else if(x-a<b&&!vis[x][a+b-x])
				q.push((node){x,a+b-x,t+1}),vis[x][a+b-x]=1;
		}
	}
	cout<<"imp";
	return 0;
}