leetcode 104. 二叉树的最大深度 递归/层序遍历

一、“见树用递归”

int maxDepth(struct TreeNode* root){
    int left, right;
    if(0 == root) return 0;
    if(0 == root->left && 0 == root->right) return 1;
    
    left = maxDepth(root->left);
    right = maxDepth(root->right);
    
    return 1+(left>right?left:right);
}

时间太久了

二、层序遍历
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class Solution {
	public:
		int maxDepth(TreeNode* root) {
			int cout =0;
			if(root == NULL) return cout;
			queue <TreeNode* > q;
			q.push(root);

			while(!q.empty()) {
				int nums = q.size();//用于记录该层有多少个元素

				while(nums >0 ) {
					TreeNode*  temp =  q.front();
					q.pop();
					if(temp->left != NULL)   q.push(temp ->left); //左孩子入队
					if(temp->right != NULL)  q.push(temp ->right); //右孩子入队
					nums--;
				}

				if(nums == 0)  cout++;   //遍历完该层
			}
			return cout;
		}
};

耗时更短