[leetcode 111] Minimum Depth of Binary Tree

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 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

 

Constraints:

• The number of nodes in the tree is in the range [0, 105].
• -1000 <= Node.val <= 1000

문제 풀이:

트리 레벨 순회

 

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    int minDepth(TreeNode* root) {
        
        
        if(!root) return 0;
        queue<TreeNode*> q;
        
        q.push(root);
        
        int minD = 0;
        while(!q.empty()){
            int size = q.size();
            minD++;
            
            for(int i=0; i<size; i++){
                TreeNode* cur = q.front();
                q.pop();
                
                if(cur->left){
                    q.push(cur->left);
                }
                
                if(cur->right){
                    q.push(cur->right);
                }
                
                if(!cur->left && !cur->right){
                    return minD;
                }
            }
        }
        
        return 0;
    }
};