# Daily Coding Challenge #35

This is a series of Daily Coding Challenge. Each day I show a few solutions written in C++. The questions are from coding practice/contest sites such as HackerRank, LeetCode, Codeforces, Atcoder and etc.

``````/*
LeetCode - Search in a Binary Search Tree

Given the root node of a binary search tree (BST) and a value. You need to find the node in the BST that the node's value equals the given value. Return the subtree rooted with that node. If such node doesn't exist, you should return NULL.

For example,

Given the tree:
4
/ \
2   7
/ \
1   3

And the value to search: 2
You should return this subtree:

2
/ \
1   3
In the example above, if we want to search the value 5, since there is no node with value 5, we should return NULL.

Note that an empty tree is represented by NULL, therefore you would see the expected output (serialized tree format) as [], not null.
*/

/**
* 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:
TreeNode* searchBST(TreeNode* root, int val) {
// search left or right branch based on the value and return the whole node directly
while(root!=nullptr&&root->val!=val){
root=(root->val>val)?root->left:root->right;
}
return root;
}
};
``````

``````/*

Write a function to check whether an input string is a valid IPv4 address or IPv6 address or neither.

IPv4 addresses are canonically represented in dot-decimal notation, which consists of four decimal numbers, each ranging from 0 to 255, separated by dots ("."), e.g.,172.16.254.1;

Besides, leading zeros in the IPv4 is invalid. For example, the address 172.16.254.01 is invalid.

IPv6 addresses are represented as eight groups of four hexadecimal digits, each group representing 16 bits. The groups are separated by colons (":"). For example, the address 2001:0db8:85a3:0000:0000:8a2e:0370:7334 is a valid one. Also, we could omit some leading zeros among four hexadecimal digits and some low-case characters in the address to upper-case ones, so 2001:db8:85a3:0:0:8A2E:0370:7334 is also a valid IPv6 address(Omit leading zeros and using upper cases).

However, we don't replace a consecutive group of zero value with a single empty group using two consecutive colons (::) to pursue simplicity. For example, 2001:0db8:85a3::8A2E:0370:7334 is an invalid IPv6 address.

Besides, extra leading zeros in the IPv6 is also invalid. For example, the address 02001:0db8:85a3:0000:0000:8a2e:0370:7334 is invalid.

Note: You may assume there is no extra space or special characters in the input string.

Example 1:
Input: "172.16.254.1"

Output: "IPv4"

Explanation: This is a valid IPv4 address, return "IPv4".
Example 2:
Input: "2001:0db8:85a3:0:0:8A2E:0370:7334"

Output: "IPv6"

Explanation: This is a valid IPv6 address, return "IPv6".
Example 3:
Input: "256.256.256.256"

Output: "Neither"

*/

class Solution {
public:
vector<string> split(string s, char c){
vector<string> parts;
string part;
istringstream iss(s);
while(getline(iss, part, c)) parts.push_back(part);
return parts;
}
bool isIPv4(string IP){
// IPv4 contains 3 dots. e.g. 172.16.254.1
if(count(IP.begin(),IP.end(),'.')!=3) return false;
vector<string> parts = split(IP,'.');
// IPv4 has 4 parts
if(parts.size()!=4) return false;
for(string part:parts){
// avoid empty part, xxxx.xxxx.xxxx.xxxx, and 012.123.123.123 cases
if(part.empty()||part.size()>3||(part.size()>1&&part=='0')) return false;
for(char c: part) {
// abc.abc.abc.abc is invalid
if(!isdigit(c)) return false;
}
// 266.255.255.255 is invalid
if(stoi(part)>255) return false;
}
return true;
}

bool isIPv6(string IP){
// IPv6 contains 7 dots. e.g. 2001:0db8:85a3:0:0:8A2E:0370:7334
if(count(IP.begin(),IP.end(),'.')!=7) return false;
vector<string> parts = split(IP,'.');
// IPv4 has 8 parts
if(parts.size()!=8) return false;
for(string part:parts){
// avoid empty part, 2002222221:0db8:85a3:0:0:8A2E:0370:7334
if(part.empty()||part.size()>4) return false;
for(char c: part) {
// 2001:0db8:85a3:0:0:8A2E:0370:733Z is invalid
if(!isdigit(c)&& (!isalpha(c)||toupper(c)>'F')) return false;
// or using isxdigit() function checking whether a character is a hexadecimal digit character (0-9, a-f, A-F) or not
// if(!isxdigit(c)) return false
}
}
return true;
}

return isIPv4(IP)?"IPv4":(isIPv6(IP)?"IPv6":"Neither");
}
};
``````

The source code is available in corresponding repo below. Star and watch for timely updates!

## wingkwong / atcoder

### Discussion   