标签：style blog io ar color 使用 sp for on
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.
解题思路：首先要注意到时间复杂度是O(n)，那么问题来了，只能扫描数组一遍，显然来不及排序了(放弃排序)，注意到只要返回一个整数，考虑使用map，对于遍历的数组中的数用hash存储，并且在端点保存连续的大小，在遍历下一个数时，看他的左右是否存在，若存在则更新端点的长度，否则，插入该数，如果该数在hash中，跳过。
class Solution { public: int longestConsecutive(vector<int> &num) { int res = 0; unordered_map<int,int> hashMap; for(auto x: num) { if(!hashMap[x])//if not exit { hashMap[x] = 1 + hashMap[x-1] + hashMap[x+1]; if(hashMap[x+1])hashMap[hashMap[x+1]+x] = hashMap[x];//update the right border if(hashMap[x-1])hashMap[x-hashMap[x-1]] = hashMap[x];//update the left border } res = max(res,hashMap[x]); } return res; } };
LeetCode Longest Consecutive Sequence
标签：style blog io ar color 使用 sp for on
原文地址：http://www.cnblogs.com/55open/p/4154542.html
