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128. 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.
class Solution { public: /*对于当前的n每次查看n-1和n+1是否已经在map中,left记录n左边的连续长度,right记录n右边的连续长度 当前长度为left+right+1 更新当前能扩展到的位置的值 */ int longestConsecutive(vector<int>& nums) { unordered_map<int,int>map; int left,right,sum,res=0; for(int n: nums){ if(!map[n]){ left=map[n-1]?map[n-1]:0; right=map[n+1]?map[n+1]:0; sum=left+right+1; map[n]=sum; res=max(res,sum); map[n-left]=sum; map[n+right]=sum; } } return res; } };
128. Longest Consecutive Sequence
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