Leetcode 题目解析之 Majority Element 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.

Hint:

• How many majority elements could it possibly have?
• Do you have a better hint? Suggest it!

因为题目中说是大于⌊ n/3 ⌋次数的元素，这样的元素最多只能有2个。

    public List<Integer> majorityElement(int[] nums) {
        List<Integer> rt = new ArrayList<Integer>();
        if (nums == null || nums.length == 0) {
            return rt;
        }
        int m1 = nums[0];
        int m2 = 0;
        int c1 = 1;
        int c2 = 0;
        for (int i = 1; i < nums.length; i++) {
            int x = nums[i];
            if (x == m1) {
                c1++;
            } else if (x == m2) {
                c2++;
            } else if (c1 == 0) {
                m1 = x;
                c1 = 1;
            } else if (c2 == 0) {
                m2 = x;
                c2 = 1;
            } else {
                c1--;
                c2--;
            }
        }
        c1 = 0;
        c2 = 0;
        for (int i = 0; i < nums.length; i++) {
            if (m1 == nums[i]) {
                c1++;
            } else if (m2 == nums[i]) {
                c2++;
            }
        }
        if (c1 > nums.length / 3) {
            rt.add(m1);
        }
        if (c2 > nums.length / 3) {
            rt.add(m2);
        }
        return rt;
    }