topic
- Given an n + 1 contains an integer array nums, which are digital (including 1 and n), found that the presence of at least one repeating integer between 1 to n. Assuming that only a unique integer, find the number of repeats.
- Example 1:
Input: [1,3,4,2,2]
Output: 2 - Example 2:
Input: [3,1,3,4,2]
Output: 3 - Note:
You can not change the original array (assuming that the array is read-only).
Only use extra space O (1) is.
It is less than the time complexity of O (n2).
Only a duplicate array of numbers, but it may be repeated more than once.
Source: stay button (LeetCode)
link: https: //leetcode-cn.com/problems/find-the-duplicate-number
copyrighted by deduction from all networks. Commercial reprint please contact the authorized official, non-commercial reprint please indicate the source.
method
class Solution {
public int findDuplicate(int[] nums) {
Set<Integer> set= new HashSet<Integer>();
for (int num : nums) {
//如果已经存在则重复了
if (set.contains(num)) {
return num;
}
set.add(num);
}
return -1;
}
}
Thinking
- using a set of judgment reciprocity
Next summary
- There is no better way to achieve the requirements described in the title?
