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.
使用递归来做
1.如果当前结点，为null。那么最小深度depth为0
2.如果当前结点不为null，那么最小深度为1
2.1 如果左结点和右结点都为null，那么到此结束，直接返回最小深度为1
2.2 如果左结点和右结点都不为null，那么需要分别计算左结点和右结点的最小深度，取较小值+1
2.3 如果左结点不为null，右结点为null，那么左结点的最小深度+1就作为，最小深度
2.4 如果右结点不为null，左结点为null，那么右结点的最小深度+1就作为，最小深度
public int MinDepth(TreeNode root) { if (root == null) { return 0; } TreeNode left = root.left; TreeNode right = root.right; if (left == null && right == null) { return 1; } int depth; if (left != null && right != null) { int leftDepth = MinDepth(left); int rightDepth = MinDepth(right); depth = Math.Min(leftDepth, rightDepth); } else if (left != null) { depth = MinDepth(left); } else { depth = MinDepth(right); } return depth + 1; }
111. Minimum Depth of Binary Tree
原文：https://www.cnblogs.com/chucklu/p/10687035.html