Leetcode之Longest Consecutive Sequence
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[LeetCode] Longest Consecutive Sequence 求最长连续序列
Given an unsorted array of integers, findthe length of the longest consecutive elements sequence.
For example,
Given [100, 4, 200, 1, 3, 2],
The longest consecutive elements sequenceis [1, 2, 3, 4]. Return its length: 4.
Your algorithm should run in O(n)complexity.
思路:
使用一个集合set存入所有的数字,然后遍历数组中的每个数字,如果其在集合中存在,那么将其移除,然后分别用两个变量pre和next算出其前一个数跟后一个数,然后在集合中循环查找,如果pre在集合中,那么将pre移除集合,然后pre再自减1,直至pre不在集合之中,对next采用同样的方法,那么next-pre-1就是当前数字的最长连续序列。
public class Solution {
publicstatic void main(String[] args) {
newSolution().longestConsecutive(new int[]{100,4,200,1,3,2});
}
publicint longestConsecutive(int[] nums) {
intres = 0;
Set<Integer>s = new HashSet<Integer>();
for(int i : nums) {
s.add(i);
}
for(int num : nums) {
if(s.remove(num)) {
intpre = num - 1;
intnext = num + 1;
while(s.remove(pre)) {
--pre;
}
while(s.remove(next)) {
++next;
}
res= Math.max(res, next - pre - 1);
}
}
returnres;
}
}
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