217. Contains Duplicate

Given an integer array nums, return true if any value appears at least twice in the array, and return false if every element is distinct.

Example 1:

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

Example 2:

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

Example 3:

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

Constraints:

• 1 <= nums.length <= 105
• -109 <= nums[i] <= 109

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哈希表

class Solution {
    public boolean containsDuplicate(int[] nums) {
        Map hashtable = new HashMap();
        for (int i = 0; i < nums.length; i++) {
            if (hashtable.containsKey(nums[i])) {
                return true;
            } else {
                hashtable.put(nums[i], 1);
            }
        }
        return false;
    }
}