原题链接https://leetcode.com/problems/longest-consecutive-sequence/
题目描述
Given an unsorted array of integers, find the length of the longest consecutive elements sequence.
Your algorithm should run in O(n) complexity.
Example:
Input: [100, 4, 200, 1, 3, 2]
Output: 4
Explanation: The longest consecutive elements sequence is [1, 2, 3, 4]. Therefore its length is 4.
Accepted
192,857
Submissions
470,536
思路分析
利用set或者Hashmap都OK
!!!一定记得会有重复元素的情况出现,别问我怎么知道的……
源码附录
class Solution {
public int longestConsecutive(int[] nums) {
if(nums == null || nums.length == 0)
{
return 0;
}
int result = 0;
HashMap<Integer,Integer> map = new HashMap<>();
for(int i:nums)
{
if(map.getOrDefault(i,0) == 0)//记得排除元素重复访问情况!……卡了好久
{
int low = map.getOrDefault(i-1,0);
int high = map.getOrDefault(i+1,0);
map.put(i,low+1+high);
if(low >= 1)
{
map.put(i-low,low+1+high);
}
if(high >= 1)
{
map.put(high+i,low+1+high);
}
result = Math.max(result,low+1+high);
}
}
return result;
}
}