217.Contains-Duplicate

217. Contains Duplicate

题目地址

https://leetcode.com/problems/contains-duplicate/

题目描述

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

代码

Approach #1 (Naive Linear Search) [Time Limit Exceeded]

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

Approach #2 Sorting

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

    return false;
  }
}

Approach #3 Hash Table

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