README.md

128. Longest Consecutive Sequence

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

Solutions (Rust)

1. Solution

use std::collections::HashMap;
use std::collections::HashSet;

impl Solution {
    pub fn longest_consecutive(nums: Vec<i32>) -> i32 {
        let mut leftmost = HashMap::new();
        let mut rightmost = HashMap::new();
        let mut ret = 0;

        for &&x in nums.iter().collect::<HashSet<_>>().iter() {
            let lo = leftmost.remove(&(x - 1)).unwrap_or(x);
            let hi = rightmost.remove(&(x + 1)).unwrap_or(x);

            leftmost.insert(hi, lo);
            rightmost.insert(lo, hi);

            ret = ret.max(hi - lo + 1);
        }

        ret
    }
}