leetcode25word-ladder

题目描述

给定两个单词（初始单词和目标单词）和一个单词字典，请找出所有的从初始单词到目标单词的最短转换序列的长度：

1. 每一次转换只能改变一个单词
2. 每一个中间词都必须存在单词字典当中

例如：

给定的初始单词start="hit"，

目标单词end ="cog"。

单词字典dict =["hot","dot","dog","lot","log"]

一个最短的转换序列为"hit" -> "hot" -> "dot" -> "dog" -> "cog",

返回长度5

注意：

如果没有符合条件的转换序列，返回0。

题目中给出的所有单词的长度都是相同的

题目中给出的所有单词都仅包含小写字母

Given two words (start and end), and a dictionary, find the length of shortest transformation sequence from start to end, such that:

1. Only one letter can be changed at a time
2. Each intermediate word must exist in the dictionary

For example,

Given:
start ="hit"
end ="cog"
dict =["hot","dot","dog","lot","log"]

As one shortest transformation is"hit" -> "hot" -> "dot" -> "dog" -> "cog",
return its length5.

Note:

• Return 0 if there is no such transformation sequence.
• All words have the same length.
  class Solution {
  public:
      int ladderLength(string start, string end, unordered_set<string> &dict) {
          queue<string>Q;
          Q.push(start);
          int res=1;
          while (!Q.empty()){
              int qsize=Q.size();
              while (qsize--){
                  string cur_front=Q.front();
                  Q.pop();
                  int size=cur_front.size();
                  for (int i=0;i<size;i++)
                  {
                      char ch=cur_front[i];
                      for (int j=0;j<26;j++){
                          cur_front[i]='a'+j;
                          if (cur_front==end) return res+1;
                          if (dict.find(cur_front)!=dict.end())
                          {
                              Q.push(cur_front);
                              dict.erase(cur_front);
                          }
                      }
                      cur_front[i]=ch;
                  }
              }
              res++;
          }
          return 0;
      }
  };