Minimum Depth of Binary Tree leetcode java

最新推荐文章于 2025-09-12 17:31:31 发布

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最新推荐文章于 2025-09-12 17:31:31 发布

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文章标签：数据结构与算法 java

本文介绍了一种求解二叉树最小深度的算法，包括递归与非递归两种实现方式。递归方法通过比较左右子树的最小深度来找到最短路径，而非递归方法则使用队列进行层次遍历。

题目：

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.

题解：

递归解法急速判断左右两边子树哪个depth最小，要注意如果有个节点只有一边孩子时，不能返回0，要返回另外一半边的depth。

递归解法：

1     public int minDepth(TreeNode root) {
2         if(root == null)
3             return 0;
4         int minleft = minDepth(root.left);
5         int minright = minDepth(root.right);
6         if(minleft==0 || minright==0)
7             return minleft>=minright?minleft+1:minright+1;
8         return Math.min(minleft,minright)+1;
9     }

非递归解法：

1     public int minDepth(TreeNode root) {
2         if(root == null)
3             return 0;
4
5         int depth = 1;//The minimum depth is the number of nodes along the shortest path from the root node down to the nearest leaf node.
6         LinkedList<TreeNode> queue = new LinkedList<TreeNode>();
7         queue.add(root);
8         int curnum = 1;
9         int nextnum = 0;
10         while(!queue.isEmpty()){
11             TreeNode cur = queue.poll();
12             curnum--;
13
14             if(cur.left == null && cur.right == null)
15                 return depth;
16
17             if(cur.left != null){
18                queue.add(cur.left);
19                nextnum++;
20             }
21
22             if(cur.right != null){
23                 queue.add(cur.right);
24                 nextnum++;
25             }
26
27             if(curnum == 0){
28                 curnum = nextnum;
29                 nextnum = 0;
30                 depth++;
31             }
32         }
33         return depth;
34     }