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.
给定一个未排序的整数数组，找长度最长的连续整数串序列，并返回长度。 复杂度要求O(n)
class Solution {
public:
int longestConsecutive(vector<int> &num) {
int size=num.size();
if(size==0)return 0;
//第一遍扫描建立前后关系map
map<int, int> exist;
for(int i=0; i<size; i++){
exist[num[i]]=1;
if(exist[num[i]-1]!=1)exist[num[i]-1]=0;
if(exist[num[i]+1]!=1)exist[num[i]+1]=0;
}
//第二遍扫描
int maxLength=0;
for(int i=0; i<size; i++){
if(exist[num[i]]==1){
//恢复串
int length=1;
int number=num[i]-1;
while(exist[number]==1){length++; exist[number]=0; number--;}
number=num[i]+1;
while(exist[number]==1){length++; exist[number]=0; number++;}
if(length>maxLength)maxLength=length;
}
}
return maxLength;
}
};LeetCode: Longest Consecutive Sequence [128],布布扣,bubuko.com
LeetCode: Longest Consecutive Sequence [128]
原文地址：http://blog.csdn.net/harryhuang1990/article/details/34126555
