single_number_ii.dart

/*



-* 137. Single Number II *-


Given an integer array nums where every element appears three times except for one, which appears exactly once. Find the single element and return it.

You must implement a solution with a linear runtime complexity and use only constant extra space.



Example 1:

Input: nums = [2,2,3,2]
Output: 3
Example 2:

Input: nums = [0,1,0,1,0,1,99]
Output: 99


Constraints:

1 <= nums.length <= 3 * 104
-231 <= nums[i] <= 231 - 1
Each element in nums appears exactly three times except for one element which appears once.

*/

import'dart:collection';

classA {
intsingleNumber(List<int> nums) {
HashMap<int, int> map =HashMap<int, int>();

for (int x in nums) {
 map[x] = (map[x] ??0) +1;
 }

for (MapEntry entry in map.entries) {
if (entry.value ==1) {
return entry.key;
 }
 }

return-1;
 }
}

classB {
intsingleNumber(List<int> nums) {
int ans =0;

for (int i =0; i <32; ++i) {
int sum =0;
for (finalint number in nums) {
 sum += (number >> i) &1;
 }
 sum %=3;
 ans |= (sum << i);
 }

// Handle negative numbers
if ((ans & (1<<31)) !=0) {
 ans =-(1<<31) | (ans & ((1<<31) -1));
 }

return ans;
 }
}

classC {
intsingleNumber(List<int> nums) {
int ones =0;
int twos =0;

for (int i =0; i < nums.length; i++) {
finalint number = nums[i];
 ones ^= (number &~twos);
 twos ^= (number &~ones);
 }

return ones;
 }
}