Merge branch 'master' of https://github.com/azl397985856/leetcode

Author: lucifer

README.en.md

@@ -139,6 +139,7 @@ The data structures mainly include:
 - [String Problems](./thinkings/string-problems-en.md)
 - [Sliding Window Technique](./thinkings/slide-window.en.md)
 - [Union Find](./thinkings/union-find.en.md) 🆕
+- [Trie](./thinkings/trie.en.md) 🆕
 
 ### Anki Flashcards
 

assets/drawio/208.implement-trie-prefix-tree.en.drawio

@@ -0,0 +1 @@
+<mxfile host="app.diagrams.net" modified="2020-07-14T05:44:32.784Z" agent="5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/83.0.4103.116 Safari/537.36" etag="spOGC2PEA06TpGs6OMPO" version="13.4.2" type="device"><diagram id="zUBkOizd3lOV14bIgwrr" name="Page-1">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</diagram></mxfile>

assets/problems/208.implement-trie-prefix-tree-1.en.png

@@ -159,11 +159,11 @@ class Solution {
         for (int i = len - 1; i >= 0; i--) {
 
             for (int j = 0; j < len - i; j++) {
-                if (checkValid(preSum, s, i, i + j))
-                    return i + 1
+                if (checkValid(preSum, s, j, i + j))
+                    return i + 1;
             }
         }
-        return 0
+        return 0;
     }
 
 

problems/1371.find-the-longest-substring-containing-vowels-in-even-counts.md

@@ -134,7 +134,7 @@ var wordBreak = function(s, wordDict) {
   dp[0] = true;
   for (let i = 0; i < s.length + 1; i++) {
     for (let word of wordDict) {
-      if (dp[i - word.length] && word.length <= i) {
+      if (word.length <= i && dp[i - word.length]) {
           if (s.substring(i - word.length, i) === word) {
             dp[i] = true;
           }

problems/139.word-break.md

@@ -69,7 +69,7 @@ JavaScript Code:
  * @return {boolean}
  */
 var searchMatrix = function(matrix, target) {
-    if (!matrix || matrix.length === 0) return 0;
+    if (!matrix || matrix.length === 0) return false;
 
     let colIndex = 0;
     let rowIndex = matrix.length - 1;

problems/240.search-a-2-d-matrix-ii.md

@@ -87,7 +87,14 @@ class Solution:
         self.visited[n] = res
         return res
 ```
+**复杂度分析**
+- 时间复杂度：一层循环是 N，另外递归深度是 N，因此总的时间复杂度是 $O(N^2)$
+- 空间复杂度：递归的栈深度和visited 的大小都是 N，因此总的空间复杂度为  $O(N)$
 
 ## 相关题目
 
-- [95.unique-binary-search-trees-ii](./95.unique-binary-search-trees-ii.md)
+- [95.unique-binary-search-trees-ii](https://github.com/azl397985856/leetcode/blob/master/problems/95.unique-binary-search-trees-ii.md)
+
+更多题解可以访问我的LeetCode题解仓库：https://github.com/azl397985856/leetcode  。 目前已经30K star啦。
+
+关注公众号力扣加加，努力用清晰直白的语言还原解题思路，并且有大量图解，手把手教你识别套路，高效刷题。

problems/96.unique-binary-search-trees.md

@@ -146,7 +146,7 @@ class Solution:
 
 ## Morris 遍历
 
-我们可以使用一种叫做 Morris 遍历的方法，既不使用递归也不借助于栈。从而在$O(1)$时间完成这个过程。
+我们可以使用一种叫做 Morris 遍历的方法，既不使用递归也不借助于栈。从而在 $O(1)$ 空间完成这个过程。
 
 ```python
 def MorrisTraversal(root):

thinkings/binary-tree-traversal.md

@@ -0,0 +1,25 @@
+## Trie
+
+When this article is done (2020-07-13), there are 17 LeetCode problems about [Trie (Prefix Tree)](https://leetcode.com/tag/trie/). Among them, 2 problems are easy, 8 are medium, and 7 are hard.
+
+Here we summarize four of them. Once you figure them out, `Trie` should not be a challenge to you anymore. Hope this article is helpful to you.
+
+The main interface of a trie should include the following:
+
+- `insert(word)`: Insert a word
+- `search(word)`: Search for a word
+- `startWith(prefix)`: Search for a word with the given prefix
+
+Among all of the above, `startWith` is one of the most essential methods, which leads to the naming for 'Prefix Tree'. You can start with [208.implement-trie-prefix-tree](https://leetcode.com/problems/implement-trie-prefix-tree) to get yourself familiar with this data structure, and then try to solve other problems.
+
+Here's the graph illustration of a trie: 
+![](../assets/problems/208.implement-trie-prefix-tree-1.en.png)
+
+As the graph shows, each node of the trie would store a character and a boolean `isWord`, which suggests whether the node is the end of a word. There might be some slight differences in the actual implementation, but they are essentially the same.
+
+### Related Problems' Solutions in this Repo (To Be Updated)
+- [0208.implement-trie-prefix-tree](https://github.com/azl397985856/leetcode/blob/b8e8fa5f0554926efa9039495b25ed7fc158372a/problems/208.implement-trie-prefix-tree.md)
+- [0211.add-and-search-word-data-structure-design](https://github.com/azl397985856/leetcode/blob/b0b69f8f11dace3a9040b54532105d42e88e6599/problems/211.add-and-search-word-data-structure-design.md)
+- [0212.word-search-ii](https://github.com/azl397985856/leetcode/blob/b0b69f8f11dace3a9040b54532105d42e88e6599/problems/212.word-search-ii.md)
+- [0472.concatenated-words](https://github.com/azl397985856/leetcode/blob/master/problems/472.concatenated-words.md)
+- [0820.short-encoding-of-words](https://github.com/azl397985856/leetcode/blob/master/problems/820.short-encoding-of-words.md)