Today I have done leetcode's September LeetCoding Challenge with cpp.

September LeetCoding Challenge 24

Description

Find the Length of the Longest Common Prefix

You are given two arrays with positive integers arr1 and arr2.

A prefix of a positive integer is an integer formed by one or more of its digits, starting from its leftmost digit. For example, 123 is a prefix of the integer 12345, while 234 is not.

A common prefix of two integers a and b is an integer c, such that c is a prefix of both a and b. For example, 5655359 and 56554 have a common prefix 565 while 1223 and 43456 do not have a common prefix.

You need to find the length of the longest common prefix between all pairs of integers (x, y) such that x belongs to arr1 and y belongs to arr2.

Return the length of the longest common prefix among all pairs. If no common prefix exists among them, return 0.

Example 1:

Input: arr1 = [1,10,100], arr2 = [1000]
Output: 3
Explanation: There are 3 pairs (arr1[i], arr2[j]):
- The longest common prefix of (1, 1000) is 1.
- The longest common prefix of (10, 1000) is 10.
- The longest common prefix of (100, 1000) is 100.
The longest common prefix is 100 with a length of 3.

Example 2:

Input: arr1 = [1,2,3], arr2 = [4,4,4]
Output: 0
Explanation: There exists no common prefix for any pair (arr1[i], arr2[j]), hence we return 0.
Note that common prefixes between elements of the same array do not count.

Constraints:

• 1 <= arr1.length, arr2.length <= 5 * 104
• 1 <= arr1[i], arr2[i] <= 108

Solution

struct TrieNode {
  bool end = false;
  TrieNode *child[10] = {};
};
void insert(TrieNode *root, const string &word) {
  TrieNode *cur = root;
  for(auto c : word) {
    if(!cur->child[c - '0']) cur->child[c - '0'] = new TrieNode();
    cur = cur->child[c - '0'];
  }
  cur->end = true;
}
int count(TrieNode *root, const string &word) {
  TrieNode *cur = root;
  int count = 0;
  for(auto c : word) {
    if(!cur->child[c - '0']) break;
    cur = cur->child[c - '0'];
    count += 1;
  }
  return count;
}
class Solution {
public:
  int longestCommonPrefix(vector<int>& arr1, vector<int>& arr2) {
    TrieNode *root = new TrieNode();
    for(auto n : arr1) {
      string s = to_string(n);
      insert(root, s);
    }
    int answer = 0;
    for(auto n : arr2) {
      string s = to_string(n);
      answer = max(answer, count(root, s));
    }
    return answer;
  }
};