'Longest Consecutive Sequence' soln

Author: joewnga

leetcode/longest_consecutive_sequence.rs

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+/// 
+/// Problem: 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 <= 10^5
+/// -10^9 <= nums[i] <= 10^9
+/// 
+
+// # Solution
+// Time complexity: O(n) 
+// Space complexity: O(n) 
+
+use std::collections::HashSet;
+
+impl Solution {
+    pub fn longest_consecutive(nums: Vec<i32>) -> i32 {
+        if nums.is_empty() {
+           return 0;
+       }
+       
+       let num_set: HashSet<i32> = nums.into_iter().collect();
+       
+       let mut max_length = 0;
+       
+       for &num in &num_set {
+           if !num_set.contains(&(num - 1)) {
+               let mut current_num = num;
+               let mut current_length = 1;
+               
+               while num_set.contains(&(current_num + 1)) {
+                   current_num += 1;
+                   current_length += 1;
+               }
+               
+               max_length = max_length.max(current_length);
+           }
+       }
+       
+       max_length
+    }
+}