LeetCode 128 最长连续序列
给定一个未排序的整数数组 nums
,找出数字连续的最长序列(不要求序列元素在原数组中连续)的长度。
请你设计并实现时间复杂度为 O(n)
的算法解决此问题。
示例 1:
输入:nums = [100,4,200,1,3,2]
输出:4
解释:最长数字连续序列是 [1, 2, 3, 4]。它的长度为 4。
示例 2:
输入:nums = [0,3,7,2,5,8,4,6,0,1]
输出:9
提示:
0 <= nums.length <= 105
-109 <= nums[i] <= 109
Solution
采用哈希集
步骤:
- 首先使用集合对数组进行去重
- 循环数列,对在数组中没有前一个连续数的数寻找它的数字连续的最长序列并记为
l
。将max_l
与l
进行比较,确定max_l
- 返回
max_l
package leetcode.editor.cn;
import java.util.HashSet;
import java.util.Set;
public class LongestConsecutiveSequence {
public static void main(String[] args) {
Solution solution = new LongestConsecutiveSequence().new Solution();
int[] a = {100, 4, 200, 1, 3, 2};
int l = a.length;
solution.longestConsecutive(a);
}
//leetcode submit region begin(Prohibit modification and deletion)
class Solution {
public int longestConsecutive(int[] nums) {
int max_l = 0;
Set<Integer> num_set = new HashSet<>();
for (int num : nums) {
num_set.add(num);
}
for (int num : nums) {
if (!num_set.contains(num - 1)) {
int currentNum = num;
int l = 1;
while (num_set.contains(currentNum + 1)) {
currentNum++;
l++;
}
max_l = Math.max(l, max_l);
}
}
return max_l;
}
private boolean isNeighbor(int a, int b) {
return Math.abs(a - b) == 1;
}
}
//leetcode submit region end(Prohibit modification and deletion)
}