Leetcode_128_Longest Consecutive Sequence
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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.
思路:
(1)题意为给定一个未排序的数组,求数组中最长连续元素的个数。
(2)由于数组是未排序的,而需要求得数组中连续序列元素的个数。首先想到的应该是对数组进行排序,本文用的是java类库中自带的排序算法:Arrays.sort()。然后遍历数组,由于数组中可能出现多个连续序列,所以设置当前最长序列个数max和正在遍历的连续序列的个数count。首先,从数组下标为0开始往后遍历,判断当前元素和后续元素是否相差1,如果相差1,则count++,当遍历到倒数第二个元素时,返回count和max的较大值;如果相等,判断max和count大小,将较大值赋给max,继续遍历;其余情况为值相差大于1,这时将max和count较大值赋给max,并将count置为1(因为连续序列在这里断开了,需要重新记录);遍历完整个数组,所得max即为最长连续序列个数。
(3)本文算法效率不是很高,有待后续优化。希望本文对你有所帮助。
算法代码实现如下:
/** * @author liqq */public class Longest_Consecutive_Sequence {public int longestConsecutive(int[] num) {if (num == null) return -1;if (num.length == 1) return 1;Arrays.sort(num);int count = 1;int max = 1;for (int i = 0; i < num.length - 1; i++) {if (num[i] + 1 == num[i + 1]) {count = count + 1;if (i == num.length - 2) {return count > max ? count : max;}} else if (num[i] == num[i + 1]) {max = count > max ? count : max;continue;} else {max = max > count ? max : count;count = 1;}}return max;}}
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