Word Ladder

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词梯:相同长度的两个单词,从源词每次更换一个字母,最终得到目标单词.

思路:BFS
将词典单词读入到集合s中.利用源单词合成Node类型,放入队列q中,并从s中删除.每次从队头取出一个单词,并从s中搜索所有的可能相邻单词(其中只有一个字母不同的单词)

满足则放入队尾并从s中删除.直到队头单词为目标单词或队列为空退出循环.

c++代码如下:

#include <iostream>#include <string>#include <queue>#include <vector>#include <stack>#include <set>#include <stdlib.h>using namespace std;struct Node{    string str;    queue<string> strqueue;    Node():str(""){}    Node(string st):str(st){}};void smallToCapital(string& a){int len=a.size();for(int i=0;i<len;i++)if(a[i]>='a'&&a[i]<='z')a[i]=a[i]-('a'-'A');}void capitalToSmall(string& a){int len=a.size();for(int i=0;i<len;i++)if(a[i]>='A'&&a[i]<='Z')a[i]=a[i]+('a'-'A');}int main(){     string c,d;    cin>>c>>d;    if(c.length()!=d.length()){    cout<<"Length not same"<<endl;    system("pause");    return -1;}    smallToCapital(c);    smallToCapital(d);    Node* a=new Node(c);    a->strqueue.push(c);    Node* b=new Node(d);    b->strqueue.push(d);    set<string> s;      string t;    freopen("D:\\in.txt","r",stdin); //字典文件    while(cin>>t){        s.insert(t);    }<span style="white-space:pre"></span>if(s.find(c)==s.end()||s.find(d)==s.end()){if(s.find(c)==s.end()) cout<<"Source word unavailable"<<endl;if(s.find(d)==s.end()) cout<<"Target word unavailable"<<endl;return -1;}    queue<Node*> q;    q.push(a);    s.erase(c);        while(!q.empty()){        if(q.front()->str==b->str){            cout<<q.front()->str<<" "<<q.size()<<endl;             cout<<"Found"<<endl;cout<<q.front()->strqueue.size()<<endl;            while((q.front()->strqueue).size()!=0){ // Output all the related strings.            capitalToSmall(q.front()->strqueue.front());cout<<q.front()->strqueue.front()<<" ";            q.front()->strqueue.pop();    }            break;        }                string tmp=q.front()->str;        int len=(q.front()->str).length();        for(int i=0;i<len;i++)        for(char c='A';c<='Z';c++)        if(c!=q.front()->str[i]){        tmp=q.front()->str;        tmp[i]=c;        set<string>::iterator it=s.find(tmp);        if(it!=s.end()){        Node* k=new Node(tmp);        k->strqueue=q.front()->strqueue;        k->strqueue.push(k->str);        q.push(k);        s.erase(*it);}}                cout<<q.front()->str<<" "<<q.size()<<" "<<endl;        q.pop();    }    if(q.empty()) cout<<"Not found"<<endl;    system("pause");

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