Diameter of Binary Tree
Given the root of a binary tree, return 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.
The length of a path between two nodes is represented by the number of edges between them.
Example 1:
Input: root = [1,2,3,4,5]
Output: 3
Explanation: 3 is the length of the path [4,2,1,3] or [5,2,1,3].
Example 2:
Input: root = [1,2]
Output: 1
Constraints:
The number of nodes in the tree is in the range [1, 104].
-100 <= Node.val <= 100
思路一：树的直径等于左子树+右子树，每次遍历节点是对比并存储最大直径
public int diameterOfBinaryTree(TreeNode root) {
maxDiameter = 0;
diameterOfBinaryTreeRec(root);
return maxDiameter;
}
private static int maxDiameter = 0;
public int diameterOfBinaryTreeRec(TreeNode root) {
if (root == null) {
return 0;
}
int left = diameterOfBinaryTreeRec(root.left);
int right = diameterOfBinaryTreeRec(root.right);
maxDiameter = Math.max(maxDiameter, left + right);
return Math.max(left, right) + 1;
}