C4_9_MajorityElementFinder.java

package com.interview.algorithms.array;

import com.interview.utils.ConsoleReader;

import java.util.ArrayList;
import java.util.List;


/**
 * Given a list, there is one element whose amount is greater or equal to the half length of the list,
 * find this element without applying additional storage space.
 *
 * @author zouzhile (zouzhile@gmail.com)
 */
public class C4_9_MajorityElementFinder {

    public static int find(Integer[] a) {
        int x = 0, cnt = 0;
        for (int i = 0; i < a.length; i++) {
            if (cnt == 0) {
                x = a[i];
                cnt++;
            } else if (a[i] == x) cnt++;
              else cnt--;
        }
        return x;
    }

    public static Integer find(List<Integer> array) {
        int index = 0;
        while (index < array.size() - 1) {
            if (array.get(index) != array.get(index + 1)) {
                array.remove(index);
                array.remove(index);
                if (index > 0) {
                    index--;
                }
            } else {
                index++;
            }
        }
        return array.get(0);
    }

    /**
     * @param args
     */
    public static void main(String[] args) {
        System.out.println("The Majority Element Finder");
        System.out.println("========================================================================");
        ConsoleReader reader = new ConsoleReader();
        System.out.print("Please input the array elements: ");
        int[] inputs = reader.readIntItems();
        List<Integer> array = new ArrayList<Integer>();
        ;
        for (int input : inputs) {
            array.add(Integer.valueOf(input));
        }
        Integer result = C4_9_MajorityElementFinder.find(array);
        System.out.println("The majority element is " + result);
    }

}