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
#include <stdio.h>
#include <stdlib.h>
#include <limits.h>
int compare(const void* a, const void* b) {
return (*(int*)a - *(int*)b);
}
int longestConsecutive(int* nums, int numsSize) {
if (numsSize == 0) {
return 0;
}
// Sort the array
qsort(nums, numsSize, sizeof(int), compare);
int max = INT_MIN;
int thsMax = 1;
for (int i = 0; i < numsSize - 1; i++) {
if (nums[i + 1] == nums[i] + 1) {
thsMax += 1;
} else if (nums[i + 1] != nums[i]) {
// Update max if current sequence is longer
if (thsMax > max) {
max = thsMax;
}
thsMax = 1; // Reset thsMax for a new sequence
}
}
// Check the last sequence length
if (thsMax > max) {
max = thsMax;
}
return max;
}