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:
Given binary tree [3,9,20,null,null,15,7]
,
3
/ \
9 20
/ \
15 7
return its minimum depth = 2.
方法一:递归
/**
* 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 == NULL)
return 0;
if(root->left != NULL && root->right!= NULL)
return 1 + min(minDepth(root->left), minDepth(root->right));
else if(root->left==NULL)
return 1 + minDepth(root->right);
else if(root->right== NULL)
return 1 + minDepth(root->left);
}
};
方法2:非递归
/**
* 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 == NULL)
return 0;
queue<TreeNode*> node;
node.push(root);
int count=0;
while(!node.empty())
{
count++;
int len = node.size();
for(int i=0;i<len;i++)
{
root = node.front();
node.pop();
if(root->left == NULL && root->right == NULL)
return count;
if(root->left)
node.push(root->left);
if(root->right)
node.push(root->right);
}
}
return count;
}
};
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