136. Single Number

Description

Given a non-empty array of integers nums, every element appears twice except for one. Find that single one.

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

 

Example 1:

Input: nums = [2,2,1]
Output: 1

Example 2:

Input: nums = [4,1,2,1,2]
Output: 4

Example 3:

Input: nums = [1]
Output: 1

 

Constraints:

  • 1 <= nums.length <= 3 * 104
  • -3 * 104 <= nums[i] <= 3 * 104
  • Each element in the array appears twice except for one element which appears only once.

Solutions

Solution 1: Bitwise Operation

The XOR operation has the following properties:

  • Any number XOR 0 is still the original number, i.e., $x \oplus 0 = x$;
  • Any number XOR itself is 0, i.e., $x \oplus x = 0$;

Performing XOR operation on all elements in the array will result in the number that only appears once.

The time complexity is $O(n)$, where $n$ is the length of the array. The space complexity is $O(1)$.

Python Code
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class Solution:
    def singleNumber(self, nums: List[int]) -> int:
        return reduce(xor, nums)

Java Code
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class Solution {
    public int singleNumber(int[] nums) {
        int ans = 0;
        for (int v : nums) {
            ans ^= v;
        }
        return ans;
    }
}

C++ Code
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class Solution {
public:
    int singleNumber(vector<int>& nums) {
        int ans = 0;
        for (int v : nums) {
            ans ^= v;
        }
        return ans;
    }
};

Go Code
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func singleNumber(nums []int) (ans int) {
	for _, v := range nums {
		ans ^= v
	}
	return
}

TypeScript Code
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function singleNumber(nums: number[]): number {
    return nums.reduce((r, v) => r ^ v);
}

Rust Code
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impl Solution {
    pub fn single_number(nums: Vec<i32>) -> i32 {
        nums.into_iter()
            .reduce(|r, v| r ^ v)
            .unwrap()
    }
}

JavaScript Code
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/**
 * @param {number[]} nums
 * @return {number}
 */
var singleNumber = function (nums) {
    return nums.reduce((a, b) => a ^ b);
};

C# Code
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public class Solution {
    public int SingleNumber(int[] nums) {
        return nums.Aggregate(0, (a, b) => a ^ b);
    }
}

C Code
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int singleNumber(int* nums, int numsSize) {
    int ans = 0;
    for (int i = 0; i < numsSize; i++) {
        ans ^= nums[i];
    }
    return ans;
}

Swift Code
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class Solution {
    func singleNumber(_ nums: [Int]) -> Int {
        return nums.reduce(0, ^)
    }
}

Solution 2

Java Code
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class Solution {
    public int singleNumber(int[] nums) {
        return Arrays.stream(nums).reduce(0, (a, b) -> a ^ b);
    }
}