Longest Consecutive Sequence 最长连续子序列

题目：

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.

解答：

哈希 空间换时间

代码：

class Solution {
public:
map<int, int> mp;
int longestConsecutive(vector<int> &num) {
int i, j;
for(i = 0; i < num.size(); i++)
mp[num[i]] = 1;
int max = 0;
for(i = 0; i < num.size(); i++)
{
int sum = 1;
if(mp.count(num[i])){
mp[num[i]] = 0;
int left = num[i] -1;
while(mp.count(left) && mp[left] != 0)
{
mp[left--] = 0;
sum++;
}
int right = num[i] + 1;
while(mp.count(right) && mp[right] != 0){
mp[right++] = 0;
sum++;
}

}
if(max < sum)
max = sum;
}
return max;
}
};