LintCode-Majority Number II

Given an array of integers, the majority number is the number that occurs more than 1/3 of the size of the array.

Find it.

Note

There is only one majority number in the array

Example

For [1, 2, 1, 2, 1, 3, 3] return 1

Challenge

O(n) time and O(1) space

Solution:

public class Solution {
    /**
     * @param nums: A list of integers
     * @return: The majority number that occurs more than 1/3
     */
    public int majorityNumber(ArrayList<Integer> nums) {
        if (nums.size()==0) return -1;
        if (nums.size()<3) return nums.get(0);
        int len = nums.size();

        int n1 = nums.get(0), n2 = 0;
        int count1 = 1, count2 = 0;

        for (int i=1;i<len;i++)
            if (nums.get(i)==n1)
                count1++;
            else if (nums.get(i)==n2)
                count2++;
            else {
                if (count1==0) {
                    n1 = nums.get(i);
                    count1 = 1;
                } else if (count2==0){
                    n2 = nums.get(i);
                    count2 = 1;
                } else {
                    count1--;
                    count2--;
                }
            }

        if (count1!=0 && count2!=0){
            count1 = 0;
            count2 = 0;
            for (int i=0; i<len;i++)
                if (nums.get(i)==n1) count1++;
                else if (nums.get(i)==n2) count2++;
            if (count1>len/3) return n1;
            else return n2;
        } else if (count1!=0) return n1;
        else return n2;
                
    }
}