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# 111. Minimum Depth of Binary Tree

## 1.問題

* 找出最小高度

![](/files/-LNL20iZ4rFrkLe2NIt9)

## 2.想法

* 提問確認題意:  
  * binary tree的類型
* function header, parameter
* test input
* 觀察
* 說明想法
  * 如果不判斷left, right, 就將node丟下去迭代, 這樣會出現一些side effect
  * 比較好的做法是判斷
    * left, right皆不存在時, sum == root->val?
    * left存在時才繼續迭代
    * right存在時才繼續迭代
    * 皆否則return false
* 測試計算複雜度

## 3.程式碼

```
/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    int minDepth(TreeNode* root) {
        if (!root) {
            return 0;
        }
        
        if (root->left && !root->right){
            return minDepth(root->left) + 1;
        } else if (root->right && !root->left){
            return minDepth(root->right) + 1;
        }
        
        return min(minDepth(root->left), minDepth(root->right)) + 1;
    }
};
```


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