Minimum Depth of Binary Tree.cpp

/* do not count NULL into the minimum depth */
class Solution {
public:
    int minDepth(TreeNode *root) {
        if (!root) return 0;
        if (!root->left && !root->right) return 1;
        if (!root->left) return minDepth(root->right)+1;
        else if (!root->right) return minDepth(root->left)+1;
        else return min(minDepth(root->left), minDepth(root->right))+1;
    }
};