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history_source/信息学奥赛一本通/3.2.2.cpp

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+#include<cstdio>
+#include<cstring>
+namespace myDef
+{
+	template<class T_queue>
+	struct Node_queue
+	{
+		T_queue num;
+		Node_queue *next=0;
+	};
+	template<class a_queue>
+	struct queue
+	{
+		Node_queue<a_queue> *head=0,*tail=0,*L=0;
+		bool isn=0;
+		int SIZE_queue;
+		void beginning()
+		{
+			head=tail=new Node_queue<a_queue>;
+			tail->next=head;
+			SIZE_queue=0;
+			isn=1;
+		}
+		queue()
+		{
+			beginning();
+		} 
+		queue(a_queue *left,a_queue *right)
+		{
+			beginning();
+			a_queue *p=left;
+			while(p!=right)
+			{
+				push(*p);
+				p++;
+			}
+		}
+		bool push(a_queue s)
+		{
+			SIZE_queue++;
+			tail->num=s;
+			if(tail->next==head)
+			{
+				tail->next=new Node_queue<a_queue>;
+				tail->next->next=head;
+				L=tail;
+				tail=tail->next;
+				return 1;
+			}
+			L=tail;
+			tail=tail->next;
+			return 0;
+		}
+		bool pop()
+		{
+			if(head==tail) return 1;
+			head=head->next;
+			SIZE_queue--;
+			return 0;
+		} 
+		a_queue& front()
+		{
+			return head->num;
+		} 
+		a_queue& back()
+		{
+			return L->num;
+		}
+		int size()
+		{
+			return SIZE_queue;
+		}
+		void clear()
+		{
+			SIZE_queue=0;
+			tail=head;
+		}
+		a_queue& operator[](unsigned int w)
+		{
+			w=w%SIZE_queue;
+			Node_queue<a_queue> *p=head;
+			for(int i=0;i<w;i++) p=p->next;
+			return p->num;
+		}
+		void operator()()
+		{
+			beginning();
+		}
+		bool empty()
+		{
+			return (SIZE_queue==0);
+		}
+		bool operator=(myDef::queue<a_queue>b)
+		{
+			if(!isn)
+			{
+				this->beginning();
+				isn=1;
+			}
+			this->clear();
+			Node_queue<a_queue> *p=b.head;
+			while(p!=b.tail)
+			{
+				this->push(p->num);
+				p=p->next;
+			}
+		}
+	};
+}
+using myDef::queue;
+struct BFS
+{
+	int floor;
+	int step;
+	BFS()
+	{
+		step=floor=0;
+	}
+	BFS(int step_,int floor_)
+	{
+		floor=floor_;
+		step=step_;
+	}
+};
+queue<BFS>bfs;
+int n,a,b;
+bool *can;
+int *num;
+bool check(int floor)
+{
+	if(floor<=0||floor>n) return 0;
+	return can[floor];
+}
+int main()
+{
+	scanf("%d%d%d",&n,&a,&b);
+	can=new bool[n+1];
+	num=new int[n+1];
+	num[0]=0;
+	for(int i=1;i<=n;i++) scanf("%d",num+i);
+	can[0]=0;
+	memset(can+1,1,n);
+	bfs.push(BFS(0,a));
+	can[a]=0;
+	if(a==b)
+	{
+		printf("0\n");
+		return 0;
+	}
+	while(bfs.size()>0)
+	{
+		if(check(bfs.front().floor+num[bfs.front().floor]))
+		{
+			bfs.push(BFS(bfs.front().step+1,bfs.front().floor+num[bfs.front().floor]));
+			if(bfs.back().floor==b)
+			{
+				printf("%d\n",bfs.back().step);
+				return 0;
+			}
+			can[bfs.back().floor]=0;
+		}
+		if(check(bfs.front().floor-num[bfs.front().floor]))
+		{
+			bfs.push(BFS(bfs.front().step+1,bfs.front().floor-num[bfs.front().floor]));
+			if(bfs.back().floor==b)
+			{
+				printf("%d\n",bfs.back().step);
+				return 0;
+			}
+			can[bfs.back().floor]=0;
+		}
+		bfs.pop();
+	}
+	printf("-1\n");
+	return 0;
+}