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# 111. Minimum Depth of Binary Tree

## 題目 :

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.

Note: A leaf is a node with no children.

### Example :

Note

Example 1:

Input: root = [3,9,20,null,null,15,7] Output: 2

Example 2:

Input: root = [2,null,3,null,4,null,5,null,6] Output: 5

#### 解題思路 :

• 這題的解法可以參考 leetcode104題解，我使用同樣queue的解法，只是多做了一個判斷當有一個node沒有left children & right children時，直接回傳depth，因為那便是最小深度

### queue解法

• time complexity: O(n) , space complexity: O(n)

Runtime: 184 ms, faster than 98.29% of Go online submissions for Minimum Depth of Binary Tree.

 `````` 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 `````` ``````/** * 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 } var queue []*TreeNode queue = append(queue,root) var depth int for len(queue) != 0 { length := len(queue) depth++ for i := 0; i < length; i++ { check := 0 node := queue if node.Left != nil { queue = append(queue, node.Left) check++ } if node.Right != nil { queue = append(queue, node.Right) check++ } if check == 0 { return depth } queue = queue[1:] } } return depth } ``````