LeetCode_217. Contains Duplicate

Posted 2021-03-25 邓戈麟

 

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.

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

 

package leetcode.easy;

public class ContainsDuplicate {
	public boolean containsDuplicate1(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;
	}
	// Time Limit Exceeded

	public boolean containsDuplicate2(int[] nums) {
		java.util.Arrays.sort(nums);
		for (int i = 0; i < nums.length - 1; ++i) {
			if (nums[i] == nums[i + 1]) {
				return true;
			}
		}
		return false;
	}

	public boolean containsDuplicate3(int[] nums) {
		java.util.Set<Integer> set = new java.util.HashSet<>(nums.length);
		for (int x : nums) {
			if (set.contains(x)) {
				return true;
			} else {
				set.add(x);
			}
		}
		return false;
	}

	@org.junit.Test
	public void test1() {
		int[] nums1 = { 1, 2, 3, 1 };
		int[] nums2 = { 1, 2, 3, 4 };
		int[] nums3 = { 1, 1, 1, 3, 3, 4, 3, 2, 4, 2 };
		System.out.println(containsDuplicate1(nums1));
		System.out.println(containsDuplicate1(nums2));
		System.out.println(containsDuplicate1(nums3));
	}

	@org.junit.Test
	public void test2() {
		int[] nums1 = { 1, 2, 3, 1 };
		int[] nums2 = { 1, 2, 3, 4 };
		int[] nums3 = { 1, 1, 1, 3, 3, 4, 3, 2, 4, 2 };
		System.out.println(containsDuplicate2(nums1));
		System.out.println(containsDuplicate2(nums2));
		System.out.println(containsDuplicate2(nums3));
	}

	@org.junit.Test
	public void test3() {
		int[] nums1 = { 1, 2, 3, 1 };
		int[] nums2 = { 1, 2, 3, 4 };
		int[] nums3 = { 1, 1, 1, 3, 3, 4, 3, 2, 4, 2 };
		System.out.println(containsDuplicate3(nums1));
		System.out.println(containsDuplicate3(nums2));
		System.out.println(containsDuplicate3(nums3));
	}
}