word_ladder

Author: hitzzc

README.md

@@ -109,6 +109,7 @@ Golang solution for leetcode. For each problem, there is a simple *_test.go to t
 #### [120. triangle](https://github.com/hitzzc/go-leetcode/tree/master/triangle)
 #### [124. binary tree maximum path sum](https://github.com/hitzzc/go-leetcode/tree/master/binary_tree_maximum_path_sum)
 #### [125. valid palindrome](https://github.com/hitzzc/go-leetcode/tree/master/valid_palindrome)
+#### [127. word ladder](https://github.com/hitzzc/go-leetcode/tree/master/word_ladder)
 
 
 

word_ladder/word_ladder.cpp

@@ -0,0 +1,49 @@
+#include <queue>
+#include <unordered_set>
+#include <map>
+#include <string>
+using namespace std;
+
+int ladderLength(string beginWord, string endWord, unordered_set<string>& wordList) {
+	if (beginWord == endWord) 
+		return 1;
+	if (distance(beginWord, endWord)==1)
+		return 2;
+	map<string, int> dist;
+	dist[beginWord] = 1;
+	queue<string> q;
+	q.push(beginWord);
+	while (!q.empty()){
+		string word = q.front();
+		q.pop();
+		if (word == endWord) return dist[word];
+		if (wordList.size() < 26*word.size()){
+			for (auto& w: wordList){
+				if (dist.find(w)==dist.end() && distance(word, w)==1){
+					dist[w] = dist[word] + 1;
+					q.push(w);
+				}
+			}
+		}else{
+			for (int i = 0; i < word.size(); ++i){
+				string temp = word;
+				for (int j = 'a'; j <= 'z'; ++j){
+					temp[i] = j;
+					if (wordList.find(temp)!=wordList.end() && dist.find(temp)==dist.end()){
+						dist[temp] = dist[word] + 1;
+						q.push(temp);
+					}
+				}
+			}
+		}
+	}
+	return 0;
+}
+
+int distance(string dist, string src){
+	int count = 0;
+	for (int i = 0; i < dist.size(); ++i){
+		if (dist[i]!=src[i]) ++count;
+	}
+	return count;
+}