Leetcode - Contains Duplicate

Given an array of integers, find if the array contains any duplicates.

Your function should return true if any value appears at least twice in the array, and it should return false if every element is distinct.

Example 1:

Input: [1,2,3,1] Output: true

Example 2:

Input: [1,2,3,4] Output: false

Example 3:

Input: [1,1,1,3,3,4,3,2,4,2] Output: true

Solution:

Solution 1:

class Solution {
    public boolean containsDuplicate(int[] nums) {
        if(nums == null || nums.length <2)
            return false;
        
        for(int i=0; i< nums.length -1;i++){
            for(int j=i+1; j< nums.length ;j++){
                if(nums[i] == nums[j])
                    return true;
            }
        }
        return false;
    }
}

Solution 2:

class Solution {
    public boolean containsDuplicate(int[] nums) {
        if(nums == null || nums.length <2)
            return false;
        
        Map<Integer,Integer> map = new HashMap();
        for(int i=0; i< nums.length;i++){
           int value = nums[i];
           if(map.get(value) == null){
               map.put(value,1);
           }else{
               return true;
           }
        }
        return false;
    }
}

Solution 3 （The most time efficient）:

class Solution {
      public boolean containsDuplicate(int[] nums) {
         Arrays.sort(nums);
         for (int i = 0; i < nums.length - 1; ++i) {
            if (nums[i] == nums[i + 1]) return true;
         }
         return false;
     }
}

Conclusion:

1.Can sort array by the embedded java library first ，it’s more efficient to work out after sorting 2.Only need to traverse array once by using HashMap or HashSet