problem
Given a binary tree, find its minimum depth.
The minimum depth is the number of nodes along the shortest path from the root node down to the nearest 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],
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/ \
9 20
/ \
15 7
return its minimum depth = 2.
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approach1:
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| class Solution {
public int minDepth(TreeNode root) {
if (root == null) {
return 0;
}
if (root.left == null || root.right == null) {
return Math.max(minDepth(root.left), minDepth(root.right)) + 1;
}
return Math.min(minDepth(root.left), minDepth(root.right)) + 1;
}
}
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复杂度