3043 - Find the Length of the Longest Common Prefix

Description

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

C++

• class Solution {
  public:
      int longestCommonPrefix(vector<int>& arr1, vector<int>& arr2) {
          unordered_set<int> s;
          for (int x : arr1) {
              for (; x; x /= 10) {
                  s.insert(x);
              }
          }
          int ans = 0;
          for (int x : arr2) {
              for (; x; x /= 10) {
                  if (s.count(x)) {
                      ans = max(ans, (int) log10(x) + 1);
                      break;
                  }
              }
          }
          return ans;
      }
  };

JAVA

• class Solution {
      public int longestCommonPrefix(int[] arr1, int[] arr2) {
          Set<Integer> s = new HashSet<>();
          for (int x : arr1) {
              for (; x > 0; x /= 10) {
                  s.add(x);
              }
          }
          int ans = 0;
          for (int x : arr2) {
              for (; x > 0; x /= 10) {
                  if (s.contains(x)) {
                      ans = Math.max(ans, String.valueOf(x).length());
                      break;
                  }
              }
          }
          return ans;
      }
  }