LeetCode-in-Java
3043. Find the Length of the Longest Common Prefix
Medium
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 * 1041 <= arr1[i], arr2[i] <= 108
Solution
public class Solution {
public int longestCommonPrefix(int[] arr1, int[] arr2) {
Trie trie = new Trie();
for (int num : arr2) {
trie.addWord(String.valueOf(num));
}
int longest = 0;
String val;
for (int num : arr1) {
val = String.valueOf(num);
if (val.length() > longest) {
longest = Math.max(longest, trie.findLongestPrefix(val));
}
}
return longest;
}
private static class Trie {
TrieNode root;
public Trie() {
root = new TrieNode();
}
public void addWord(String word) {
TrieNode first = root;
int codePoint;
for (int i = 0; i < word.length(); i++) {
codePoint = word.charAt(i) - '0';
if (first.nodes[codePoint] == null) {
first.nodes[codePoint] = new TrieNode();
}
first = first.nodes[codePoint];
}
}
public int findLongestPrefix(String word) {
TrieNode first = root;
int i = 0;
int codePoint;
while (i < word.length()) {
codePoint = word.charAt(i) - '0';
if (first.nodes[codePoint] == null) {
return i;
}
first = first.nodes[codePoint];
i++;
}
return i;
}
}
private static class TrieNode {
TrieNode[] nodes;
public TrieNode() {
nodes = new TrieNode[10];
}
}
}