'Single Number II' soln

Author: joewnga

leetcode/single_number_ii.rs

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+/// 
+/// Problem: 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 * 10^4
+/// -2^31 <= nums[i] <= 2^31 - 1
+/// Each element in nums appears exactly three times except for one element which appears once.
+/// 
+
+// # Solution
+// Time complexity: O(n) 
+// Space complexity: O(1) 
+
+impl Solution {
+    pub fn single_number(nums: Vec<i32>) -> i32 {
+       let mut ones = 0;
+       let mut twos = 0;
+       
+       for num in nums {
+           ones = (ones ^ num) & !twos;
+           twos = (twos ^ num) & !ones;
+           
+       }
+       ones
+    }
+}