算法第十四周作业01

Description

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.

Solution

• 首先对输入数组排序
• count表示局部有续子串长度，result表示最大有序子串长度（即返回的结果）
• 逐个迭代，当nums[i] == nums[i-1] + 1时，count++；当nums[i] == nums[i-1]时，跳过，不处理；否则，nums[i]和nums[i-1]不连续且不相等，则局部有序终止了，重置count。

Code

import java.util.Arrays;

public class Solution {
    public int longestConsecutive(int[] nums) {
        // 初始化
        int result = nums.length == 0 ? 0 : 1;
        int count = 1;
        // 排序
        Arrays.sort(nums);
        // 逐个迭代判断
        for (int i = 0; i < nums.length - 1; i++) {
            if (nums[i + 1] == nums[i]+1) {
                // 计数器加1
                count++;
                if (result < count)
                    result = count;
            } else if(nums[i+1] != nums[i]) {
                // 重置计数器
                count = 1;
            }
        }
        return result;
    }
}