543 Diameter of Binary Tree

543. Diameter of Binary Tree

1. Question

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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1
2
/ \
3
2 3
4
/ \
5
4 5
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Return 3, which is the length of the path [4,2,1,3] or [5,2,1,3].

2. Implementation

(1) DFS
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class Solution {
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public int diameterOfBinaryTree(TreeNode root) {
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int[] max = new int[1];
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getMaxDepth(root, max);
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return max[0];
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}
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public int getMaxDepth(TreeNode node, int[] max) {
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if (node == null) {
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return 0;
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}
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int maxLeftDepth = getMaxDepth(node.left, max);
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int maxRightDepth = getMaxDepth(node.right, max);
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max[0] = Math.max(max[0], maxLeftDepth + maxRightDepth);
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return 1 + Math.max(maxLeftDepth, maxRightDepth);
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}
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}
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3. Time & Space Complexity

DFS: 时间复杂度: O(n), 空间复杂度: O(h)