problem

Given a binary tree, find its maximum depth.

The maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.

Note: A leaf is a node with no children.

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Example:

Given binary tree [3,9,20,null,null,15,7],

3
/ \
9 20
/ \
15 7
return its depth = 3.

approach1:

深度优先

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class Solution {
public int maxDepth(TreeNode root) {
if (root == null) {
return 0;
}
return 1 + Math.max(maxDepth(root.left), maxDepth(root.right));

}
}

复杂度

  • time:O(n)
  • space:O(n)

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