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543. Diameter of Binary Tree
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
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/ \
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.
解题分析
这道题就是一个深度优先搜索。不同之处在于，要在遍历过程中，把直径的最大值保存下来。同时，还要返回子树中最长的路径。
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/**
* Runtime: 0 ms, faster than 100.00% of Java online submissions for Diameter of Binary Tree.
* Memory Usage: 39 MB, less than 19.48% of Java online submissions for Diameter of Binary Tree.
*/
private int result;
public int diameterOfBinaryTree(TreeNode root) {
result = 1;
dfs(root);
return result - 1;
}
private int dfs(TreeNode root) {
if (Objects.isNull(root)) {
return 0;
}
int left = dfs(root.left);
int right = dfs(root.right);
result = Math.max(result, left + right + 1);
return Math.max(left, right) + 1;
}