Minimum Depth of Binary Tree

Problem: Minimum Depth of Binary Tree

We can do breadth-first search to find the nearest leaf node. During the search, we can record the depth of each level so that once we find a leaf node we can immediately return the answer.

Code in Python:

class Solution(object):
    def minDepth(self, root):
        """
        :type root: TreeNode
        :rtype: int
        """
        if not root: return 0
        ans, currentLevel = 1, [root]
        while currentLevel:
            nextLevel = []
            for node in currentLevel:
                if not node.left and not node.right: return ans
                if node.left: nextLevel.append(node.left)
                if node.right: nextLevel.append(node.right)
            ans, currentLevel = ans + 1, nextLevel
        return ans