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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

解題思路

一樣用hash map 統計有無重複出現的

class Solution {
    public boolean containsDuplicate(int[] nums) {
        HashMap<Integer, Integer> hashmap = new HashMap<>();
        int len = nums.length;

        for(int i = 0; i < len; i ++) {
            hashmap.put(nums[i], hashmap.getOrDefault(nums[i], 0) + 1);
            if (hashmap.get(nums[i]) > 1) {
                return true;
            }
        }
 
        return false;
    }
}