LeetCode-in-All
128. Longest Consecutive Sequence
Medium
Given an unsorted array of integers nums, return the length of the longest consecutive elements sequence.
You must write an algorithm that runs in O(n) time.
Example 1:
Input: nums = [100,4,200,1,3,2]
Output: 4
Explanation: The longest consecutive elements sequence is [1, 2, 3, 4]. Therefore its length is 4.
Example 2:
Input: nums = [0,3,7,2,5,8,4,6,0,1]
Output: 9
Constraints:
0 <= nums.length <= 105-109 <= nums[i] <= 109
Solution
class Solution {
int longestConsecutive(List<int> nums) {
if (nums.isEmpty) {
return 0;
}
nums.sort(); // Sort the list
int max = -999999999; // Equivalent to Integer.MIN_VALUE in Java
int currentMax = 1;
for (int i = 0; i < nums.length - 1; i++) {
if (nums[i + 1] == nums[i] + 1) {
currentMax += 1;
continue;
}
if (nums[i + 1] == nums[i]) {
continue;
}
// Start of a new sequence
max = maxVal(max, currentMax);
currentMax = 1;
}
return maxVal(max, currentMax);
}
int maxVal(int a, int b) => a > b ? a : b; // Utility function for max
}