LeetCode-in-Java
2501. Longest Square Streak in an Array
Medium
You are given an integer array nums. A subsequence of nums is called a square streak if:
- The length of the subsequence is at least
2, and - after sorting the subsequence, each element (except the first element) is the square of the previous number.
Return the length of the longest square streak in nums, or return -1 if there is no square streak.
A subsequence is an array that can be derived from another array by deleting some or no elements without changing the order of the remaining elements.
Example 1:
Input: nums = [4,3,6,16,8,2]
Output: 3
Explanation: Choose the subsequence [4,16,2]. After sorting it, it becomes [2,4,16].
-
4 = 2 * 2.
-
16 = 4 * 4.
Therefore, [4,16,2] is a square streak.
It can be shown that every subsequence of length 4 is not a square streak.
Example 2:
Input: nums = [2,3,5,6,7]
Output: -1
Explanation: There is no square streak in nums so return -1.
Constraints:
2 <= nums.length <= 1052 <= nums[i] <= 105
Solution
public class Solution {
public int longestSquareStreak(int[] nums) {
int result = -1;
final int max = 100000;
boolean[] isExisted = new boolean[max + 1];
boolean[] isVisited = new boolean[max + 1];
for (int num : nums) {
isExisted[num] = true;
}
for (int i = 2; i * i <= max; i++) {
if (!isExisted[i] || isVisited[i]) {
continue;
}
isVisited[i] = true;
int length = 1;
int j = i * i;
while (j >= 0 && j <= max && isExisted[j]) {
isVisited[j] = true;
length++;
j = j * j;
}
if (length > 1) {
result = Math.max(result, length);
}
}
return result;
}
}