[LeetCode][JavaScript]Longest Consecutive Sequence

Longest Consecutive Sequence

Given an unsorted array of integers, find the length of the longest consecutive elements sequence.

For example,
Given [100, 4, 200, 1, 3, 2],
The longest consecutive elements sequence is [1, 2, 3, 4]. Return its length: 4.

Your algorithm should run in O(n) complexity.

https://leetcode.com/problems/longest-consecutive-sequence/

 

 

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排序一下就是O(nlogn)了，真心没想出如何O(n)。

看了一下说set的查找，插入，删除都是O(1)。

set的操作难道不是O(logn)吗，我读书少你们别骗我。

好吧，O(n)+O(n)还是O(n)。

无论如何，这题不算hard吧，边界情况也很明确，无非就是longestConsecutive([])和longestConsecutive([1])。

 

/**
 * @param {number[]} nums
 * @return {number}
 */
var longestConsecutive = function(nums) {
    var set = new Set();
    for(var i = 0; i < nums.length; i++){
        if(!set.has(nums[i])){
            set.add(nums[i]);
        }
    }
    var max = 0;
    var count = 0;
    for(i in nums){
        curr = nums[i];
        if(set.has(nums[i])){
            count = 1;
            set.delete(nums[i]);
        }        
        while(set.has(curr - 1)){
            if(set.has(curr - 1)){
                count ++;
                set.delete(curr - 1);
                curr -= 1;
            }   
        }
        curr = nums[i];
        while(set.has(curr + 1)){
            if(set.has(curr + 1)){
                count ++;
                set.delete(curr + 1);
                curr += 1;
            }   
        }

        if(count > max){
            max = count;
        }
    }

    return max;
};