Question

Given a non-empty array of integers, every element appears three times except for one, which appears exactly once. Find that single one.

Note:

Your algorithm should have a linear runtime complexity. Could you implement it without using extra memory?

Example 1:

Input: [2,2,3,2]
Output: 3

Example 2:

Input: [0,1,0,1,0,1,99]
Output: 99

Thinking:

  • Method 1:sort
class Solution {
    public int singleNumber(int[] nums) {
        Arrays.sort(nums);
        if(nums.length > 1)
            if(nums[0] != nums[1]) return nums[0];
        for(int i = 1; i < nums.length - 1; i++){
            if(nums[i] != nums[i - 1] && nums[i] != nums[i + 1])
                return nums[i];
        }
        return nums[nums.length - 1];
    }
}

二刷

  1. 排序 
    class Solution {
 public int singleNumber(int[] nums) {
     Arrays.sort(nums);
     if(nums.length > 1){
         if(nums[0] != nums[1])
             return nums[0];
     }
     for(int i = 1; i < nums.length - 1; i++){
         if(nums[i] != nums[i - 1] && nums[i] != nums[i + 1])
             return nums[i];
     }
     return nums[nums.length - 1];
 }
}