java_contain_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.

Examples

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 <= $10^5$
• $-10^9$ <= nums[i] <= $10^9$

解析

給定一個整數陣列 nums 要求寫一個演算法去判斷是否有重複值

可以透過 hashSet 來紀錄每次出現過的值 每次只要發現 hashSet 有出現過的值 就直接回傳 true

時間複雜度為 O(n) 空間複雜度為 O(n)

程式碼

import java.util.HashSet;

public class Solution {
    public boolean containDuplicate(int[] nums) {
        HashSet<Integer> hash = new HashSet<>();
        for (int num : nums) {
            if (hash.contains(num)) {
                return true;
            }
            hash.add(num);
        }
        return false;
    }
}

困難點

1. 理解 HashTable 作用

Solve Point

• Understand what problem to solve
• Analysis Complexity