/**
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
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*/
//leetcode submit region begin(Prohibit modification and deletion)
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode() {}
* TreeNode(int val) { this.val = val; }
* TreeNode(int val, TreeNode left, TreeNode right) {
* this.val = val;
* this.left = left;
* this.right = right;
* }
* }
*/
class Solution {
public int diameterOfBinaryTree(TreeNode root) {
if (root == null) {
return 0;
}
Map<TreeNode, Integer> rootLenMap = new HashMap<>();
Map<TreeNode, Integer> maxLenMap = new HashMap<>();
return getMaxLen(maxLenMap, rootLenMap, root) - 1;
}
private int getRootLen(Map<TreeNode, Integer> rootLenMap, TreeNode root) {
int len = 0;
if (root != null) {
int leftLen = getRootLen(rootLenMap, root.left);
int rightLen = getRootLen(rootLenMap, root.right);
len = Math.max(leftLen, rightLen) + 1;
}
rootLenMap.put(root, len);
return len;
}
private int getMaxLen(Map<TreeNode, Integer> maxLenMap, Map<TreeNode, Integer> rootLenMap, TreeNode root) {
int len = 0;
if (root != null) {
int leftLen = getRootLen(rootLenMap, root.left);
int rightLen = getRootLen(rootLenMap, root.right);
int leftMax = getMaxLen(maxLenMap, rootLenMap, root.left);
int rightMax = getMaxLen(maxLenMap, rootLenMap, root.right);
len = Math.max(leftLen + rightLen + 1, Math.max(leftMax, rightMax));
}
maxLenMap.put(root, len);
return len;
}
}
//leetcode submit region end(Prohibit modification and deletion)
