287. Find the Duplicate Number
Given an array of integers nums containing n + 1 integers where each integer is in the range [1, n] inclusive.
There is only one repeated number in nums, return this repeated number.
Example 1:
Input: nums = [1,3,4,2,2]
Output: 2
Example 2:
Input: nums = [3,1,3,4,2]
Output: 3
Example 3:
Input: nums = [1,1]
Output: 1
Example 4:
Input: nums = [1,1,2]
Output: 1
Constraints:
- 2 <= n <= 3 * 104
- nums.length == n + 1
- 1 <= nums[i] <= n
- All the integers in nums appear only once except for precisely one integer which appears two or more times.
Follow up:
- How can we prove that at least one duplicate number must exist in nums?
- Can you solve the problem without modifying the array nums?
- Can you solve the problem using only constant, O(1) extra space?
- Can you solve the problem with runtime complexity less than O(n2)?
最简单使用HashSet
class Solution {
public int findDuplicate(int[] nums) {
if(nums.length<=1)
return 0;
Set<Integer> set = new HashSet<>();
for(int n : nums){
if(!set.add(n)) return n;
}
return -1;
}
}数组存储相同元素
class Solution {
public int findDuplicate(int[] nums) {
int[] duplicate = new int[nums.length];
for(int i=0;i<nums.length;i++){
duplicate[nums[i]]++;
}
for(int i=0;i<duplicate.length;i++){
if(duplicate[i]>1){
return i;
}
}
return -1;
}
}