feat: add 543

Author: Blankj

README.md

@@ -50,6 +50,7 @@
 |119|[Pascal's Triangle II][119]|Array|
 |121|[Best Time to Buy and Sell Stock][121]|Array, Dynamic Programmin|
 |122|[Best Time to Buy and Sell Stock II][122]|Array, Greedy|
+|543|[Diameter of Binary Tree][543]|Tree|
 
 
 ## Medium
@@ -108,10 +109,12 @@
 [119]: https://github.com/Blankj/awesome-java-leetcode/blob/master/note/119/README.md
 [121]: https://github.com/Blankj/awesome-java-leetcode/blob/master/note/121/README.md
 [122]: https://github.com/Blankj/awesome-java-leetcode/blob/master/note/122/README.md
+[543]: https://github.com/Blankj/awesome-java-leetcode/blob/master/note/543/README.md
 
 [002]: https://github.com/Blankj/awesome-java-leetcode/blob/master/note/002/README.md
 [003]: https://github.com/Blankj/awesome-java-leetcode/blob/master/note/003/README.md
 [008]: https://github.com/Blankj/awesome-java-leetcode/blob/master/note/008/README.md
 [019]: https://github.com/Blankj/awesome-java-leetcode/blob/master/note/019/README.md
+[554]: https://github.com/Blankj/awesome-java-leetcode/blob/master/note/554/README.md
 
 [004]: https://github.com/Blankj/awesome-java-leetcode/blob/master/note/004/README.md

note/543/README.md

@@ -0,0 +1,66 @@
+# [Diameter of Binary Tree][title]
+
+## Description
+
+Given a binary tree, you need to compute the length of the diameter of the tree. The diameter of a binary tree is the length of the **longest** path between any two nodes in a tree. This path may or may not pass through the root.
+
+**Example:**
+Given a binary tree
+
+```
+          1
+         / \
+        2   3
+       / \     
+      4   5    
+
+```
+
+Return **3**, which is the length of the path [4,2,1,3] or [5,2,1,3].
+
+**Note:** The length of path between two nodes is represented by the number of edges between them.
+
+**Tags:** Tree
+
+
+## 思路
+
+题意是让你算出二叉树中最远的两个节点的距离，分别计算左右子树的最大高度，然后不断迭代出其和的最大值就是最终结果。
+
+``` java
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     int val;
+ *     TreeNode left;
+ *     TreeNode right;
+ *     TreeNode(int x) { val = x; }
+ * }
+ */
+class Solution {
+    int max = 0;
+
+    public int diameterOfBinaryTree(TreeNode root) {
+        helper(root);
+        return max;
+    }
+
+    private int helper(TreeNode root) {
+        if (root == null) return 0;
+        int l = helper(root.left);
+        int r = helper(root.right);
+        if (l + r > max) max = l + r;
+        return Math.max(l, r) + 1;
+    }
+}
+```
+
+
+## 结语
+
+如果你同我一样热爱数据结构、算法、LeetCode，可以关注我GitHub上的LeetCode题解：[awesome-java-leetcode][ajl]
+
+
+
+[title]: https://leetcode.com/problems/diameter-of-binary-tree
+[ajl]: https://github.com/Blankj/awesome-java-leetcode

project/leetcode/.idea/workspace.xml

@@ -0,0 +1,34 @@
+package com.blankj.easy._543;
+
+
+import com.blankj.structure.TreeNode;
+
+/**
+ * <pre>
+ *     author: Blankj
+ *     blog  : http://blankj.com
+ *     time  : 2017/10/13
+ *     desc  :
+ * </pre>
+ */
+public class Solution {
+    int max = 0;
+
+    public int diameterOfBinaryTree(TreeNode root) {
+        helper(root);
+        return max;
+    }
+
+    private int helper(TreeNode root) {
+        if (root == null) return 0;
+        int l = helper(root.left);
+        int r = helper(root.right);
+        if (l + r > max) max = l + r;
+        return Math.max(l, r) + 1;
+    }
+
+    public static void main(String[] args) {
+        Solution solution = new Solution();
+        System.out.println(solution.diameterOfBinaryTree(TreeNode.createTestData("[1,2,3,4,5]")));
+    }
+}