Minimum Binary Tree depth

Ideas: Recursive method.

Input: Root Node of a binary tree;

Output: Minimum depth of a binary tree.

Minimum depth Definition: Number of nodes in the shortest path from the root node to the leaf node.

The algorithm is as follows::

Binary Trees are divided into the following situations:

• The input root node is empty and return null;
• The input root node is not empty, the left subtree is empty, and the right subtree is empty. The minimum depth 1 is returned;
• The input root node is not empty, the left subtree is empty, and the right subtree is not empty. The minimum depth + 1 of the right subtree is returned;
• The input root node is not empty, the left subtree is not empty, and the right subtree is empty. The minimum depth + 1 of the Left subtree is returned;
• If the input root node is not empty and left and right subtree is not empty, a smaller value + 1 is returned for the left and right subtree.

The Code is as follows::

/** * Definition for binary tree * 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 NULL;        if(root->left==NULL && root->right == NULL) return 1;        else if(root->left == NULL && root->right !=NULL) return minDepth(root->right)+1;        else if(root->left !=NULL && root->right ==NULL) return minDepth(root->left)+1;        else if(root->left !=NULL && root->right != NULL) return minDepth(root->left)<=minDepth(root->right)?(minDepth(root->left)+1):(minDepth(root->right)+1);    } };