day 9

Author: sachuverma

Leetcode Daily Challenge/January-2021/09. Word Ladder.cpp

@@ -0,0 +1,79 @@
+/*
+Word Ladder
+===========
+
+A transformation sequence from word beginWord to word endWord using a dictionary wordList is a sequence of words such that:
+
+The first word in the sequence is beginWord.
+The last word in the sequence is endWord.
+Only one letter is different between each adjacent pair of words in the sequence.
+Every word in the sequence is in wordList.
+Given two words, beginWord and endWord, and a dictionary wordList, return the number of words in the shortest transformation sequence from beginWord to endWord, or 0 if no such sequence exists.
+
+Example 1:
+Input: beginWord = "hit", endWord = "cog", wordList = ["hot","dot","dog","lot","log","cog"]
+Output: 5
+Explanation: One shortest transformation is "hit" -> "hot" -> "dot" -> "dog" -> "cog" with 5 words.
+
+Example 2:
+Input: beginWord = "hit", endWord = "cog", wordList = ["hot","dot","dog","lot","log"]
+Output: 0
+Explanation: The endWord "cog" is not in wordList, therefore there is no possible transformation.
+
+Constraints:
+1 <= beginWord.length <= 10
+endWord.length == beginWord.length
+1 <= wordList.length <= 5000
+wordList[i].length == beginWord.length
+beginWord, endWord, and wordList[i] consist of lowercase English letters.
+beginWord != endWord
+All the strings in wordList are unique.
+*/
+
+class Solution
+{
+public:
+  int ladderLength(string beginWord, string endWord, vector<string> &wordList)
+  {
+    unordered_set<string> left(wordList.begin(), wordList.end());
+
+    if (left.find(endWord) == left.end())
+      return 0;
+    int ans = 0;
+
+    queue<string> pending;
+    pending.push(beginWord);
+
+    while (pending.size())
+    {
+      int size = pending.size();
+      ans++;
+
+      for (int i = 0; i < size; ++i)
+      {
+        auto curr = pending.front();
+        pending.pop();
+
+        for (int i = 0; i < curr.size(); ++i)
+        {
+          auto temp = curr;
+          for (auto c = 'a'; c <= 'z'; ++c)
+          {
+            temp[i] = c;
+            if (temp == curr)
+              continue;
+            if (temp == endWord)
+              return ans + 1;
+            if (left.find(temp) != left.end())
+            {
+              left.erase(temp);
+              pending.push(temp);
+            }
+          }
+        }
+      }
+    }
+
+    return 0;
+  }
+};

Leetcode Daily Challenge/January-2021/README.md

@@ -9,7 +9,7 @@
 | 5.  | [Remove Duplicates from Sorted List II](https://leetcode.com/explore/challenge/card/january-leetcoding-challenge-2021/579/week-1-january-1st-january-7th/3593/) | [cpp](./05.%20Remove%20Duplicates%20from%20Sorted%20List%20II.cpp) |
 | 6.  | [Kth Missing Positive Number](https://leetcode.com/explore/challenge/card/january-leetcoding-challenge-2021/579/week-1-january-1st-january-7th/3594/) | [cpp](./06.%20Kth%20Missing%20Positive%20Number.cpp) |
 | 7.  | [Longest Substring Without Repeating Characters](https://leetcode.com/explore/challenge/card/january-leetcoding-challenge-2021/579/week-1-january-1st-january-7th/3595/) | [cpp](./07.%20Longest%20Substring%20Without%20Repeating%20Characters.cpp) |
-| .8  | [Check If Two String Arrays are Equivalent](https://leetcode.com/explore/challenge/card/january-leetcoding-challenge-2021/580/week-2-january-8th-january-14th/3597/) | [cpp](./08.%20Check%20If%20Two%20String%20Arrays%20are%20Equivalent.cpp) |
-| .  | []() | [cpp](./.%20.cpp) |
+| 8.  | [Check If Two String Arrays are Equivalent](https://leetcode.com/explore/challenge/card/january-leetcoding-challenge-2021/580/week-2-january-8th-january-14th/3597/) | [cpp](./08.%20Check%20If%20Two%20String%20Arrays%20are%20Equivalent.cpp) |
+| 9.  | [Word Ladder](https://leetcode.com/explore/challenge/card/january-leetcoding-challenge-2021/580/week-2-january-8th-january-14th/3598/) | [cpp](./09.%20Word%20Ladder.cpp) |
 | .  | []() | [cpp](./.%20.cpp) |
 | .  | []() | [cpp](./.%20.cpp) |