217. Contains Duplicate (Easy)

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.

Solution:

Java:

import java.util.HashMap;import java.util.Map;public class Solution {    public static boolean containsDuplicate(int[] nums) {        Map<Integer, Integer> map = new HashMap<>();        for(int i = 0; i < nums.length; i++) {            if(map.get(nums[i]) == null) {                map.put(nums[i], i);            } else {                return true;            }        }        return false;    }    public static void main(String[] args) {        int[] arr = {1, 1, 3, 5, 6};        System.out.println(containsDuplicate(arr));    }}

使用HashMap存储[值，下标]，如果发现值对应的下标已存在，则表示该值重复出现在数组中。