README_EN.md

137. Single Number II

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Description

Given a non-empty array of integers, every element appears three times except for one, which appears exactly once. Find that single one.

Note:

Your algorithm should have a linear runtime complexity. Could you implement it without using extra memory?

Example 1:

Input: [2,2,3,2]

Output: 3

Example 2:

Input: [0,1,0,1,0,1,99]

Output: 99

Solutions

Python3

class Solution:
    def singleNumber(self, nums: List[int]) -> int:
        bits = [0] * 32
        for num in nums:
            for i in range(32):
                bits[i] += (num & 1)
                num >>= 1
        res = 0
        for i in range(32):
            if bits[i] % 3 != 0:
                res += (1 << i)
        return res if bits[31] % 3 == 0 else ~(res ^ 0xffffffff)

Java

class Solution {
    public int singleNumber(int[] nums) {
        int[] bits = new int[32];
        for (int num : nums) {
            for (int i = 0; i < 32; ++i) {
                bits[i] += (num & 1);
                num >>= 1;
            }
        }

        int res = 0;
        for (int i = 0; i < 32; ++i) {
            if (bits[i] % 3 == 1) {
                res += (1 << i);
            }
        }
        return res;
    }
}

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