LeetCode: MajorityElement II

LeetCode: MajorityElement II

Given an integer array of size n, find all elements that appear more than ⌊ n/3 ⌋ times.

The algorithm should run in linear time and in O(1) space.

Solution:

要点就是摩尔投票法: https://www.zhihu.com/question/49973163 

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public class MajorityElementII {
    public List<Integer> majorityElement(int[] nums) {
        int a, b, ca, cb;
        a = b = ca = cb = 0;
        for (int n : nums) {
            if(n == a) ca++;
            else if (n == b) cb++;
            else if(ca == 0) {a = n;ca++;}
            else if(cb == 0) {b = n;cb++;}
            else {ca--;cb--;}
        }

        ca = cb = 0;
        for (int n : nums) {
            if (n == a) ca++;
            else if (n == b) cb++;
        }
        List<Integer> result = new ArrayList<>();
        if (ca > nums.length / 3) result.add(a);
        if (cb > nums.length / 3) result.add(b);
        return result;
    }
}