Question
Given an array of integers, 1 ≤ a[i] ≤ n (n = size of array), some elements appear twice and others appear once.
Find all the elements that appear twice in this array.
Could you do it without extra space and in O(n) runtime?
Example:
Input: [4,3,2,7,8,2,3,1] Output: [2,3]
Difficulty:Medium
Category:Array
Analyze
Solution
class Solution {
public:
vector<int> findDuplicates(vector<int>& nums) {
vector<int> res;
vec_sort(nums);
for (int i = 0; i < nums.size(); ++i) {
if (nums[i] != i + 1) res.emplace_back(nums[i]);
}
return res;
}
void vec_sort(vector<int>& nums) {
// Build a array to store the numsbers
const unsigned int len_n = nums.size();
for (int i = 0; i < len_n; ++i) {
while (nums[i] != i + 1) {
if (nums[i] <= 0 || nums[i] > len_n || nums[i] == nums[nums[i] - 1]) break;
swap(nums[i], nums[nums[i] - 1]);
}
}
}
};
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