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single-element-in-sorted-array.cpp
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64 lines (54 loc) · 1.56 KB
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#include <bits/stdc++.h>
using namespace std;
class Solution {
public:
// bruteforce
/* int singleNonDuplicate(vector<int> &nums) {
for (int i=0; i<nums.size()-1; i+=2) {
if (nums[i] == nums[i+1]) {
continue;
} else {
return nums[i];
}
}
return -1;
} */
// bruteforce using XOR
/* int singleNonDuplicate(vector<int> &nums) {
int ans = 0;
for (int i=0; i<nums.size(); i++) {
ans = ans ^ nums[i];
}
return ans;
} */
// binary search
int singleNonDuplicate(vector<int> &nums) {
int n = nums.size();
// edge cases
if (n == 1) return nums[0];
if (nums[0] != nums[1]) return nums[0];
if (nums[n-1] != nums[n-2]) return nums[n-1];
int low = 1;
int high = n-2;
while(low <= high) {
int mid = (low + high) / 2;
// check if mid is the non duplicate element
if (nums[mid] != nums[mid-1] && nums[mid] != nums[mid+1]) {
return nums[mid];
}
// other conditions
if ((mid % 2 == 1 && nums[mid-1] == nums[mid]) || (mid % 2 == 0 && nums[mid] == nums[mid+1])) {
// left to mid is sorted
low = mid + 1;
} else {
high = high - 1;
}
}
return -1;
}
};
int main() {
Solution s1;
vector<int> nums = {1, 1, 2, 2, 3, 3, 4, 4, 5, 6, 6};
cout << s1.singleNonDuplicate(nums);
}