111. Minimum Depth of Binary Tree #

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.

Example:

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

    3
   / \
  9  20
    /  \
   15   7

return its minimum depth = 2.

Problem Summary #

Given a binary tree, find its minimum depth. The minimum depth is the number of nodes along the shortest path from the root node to the nearest leaf node. Note: A leaf node refers to a node with no child nodes.

Solution Approach #

• Recursively calculate the depth from the root node to the leaf nodes, and output the minimum value

Code #

package leetcode

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func minDepth(root *TreeNode) int {
	if root == nil {
		return 0
	}
	if root.Left == nil {
		return minDepth(root.Right) + 1
	}
	if root.Right == nil {
		return minDepth(root.Left) + 1
	}
	return min(minDepth(root.Left), minDepth(root.Right)) + 1
}