剑指offer-数组中出现次数超过一半的数字

import java.util.HashMap;

public class Solution {
    public int MoreThanHalfNum_Solution(int [] array) {
        HashMap<Integer, Integer> map = new HashMap<>();
        if (array.length == 1) return array[0];
        for (int i = 0; i < array.length; i++) {
            if (map.containsKey(array[i])) {
                int count = map.get(array[i]);
                if (count >= array.length / 2)
                    return array[i];
                map.put(array[i], count + 1);
            }
            else {
                map.put(array[i], 1);
            }
        }
        return 0;
    }
}

public class Solution {
    public int MoreThanHalfNum_Solution(int [] array) {
        if (array.length == 0) return 0;
        if (array.length == 1) return array[0];
        int left = 0;
        int right = array.length - 1;
        
        while (left < right) {
            int index = position(array, left, right);
            if (index == array.length / 2) {
                if (checkMoreThanHalf(array, array[index]))
                    return array[index];
                else 
                    return 0;
            }
                
            else if (index < array.length / 2)
                left = index + 1;
            else 
                right = index - 1;
        }
        
        return 0;
    }
    
    private int position(int[] array, int start, int end) {
        int index = start + (int)Math.random() * (end - start);
        swap(array, index, end);
        
        int small = start - 1;
        for (int i = start; i < end; i++) {
            if (array[i] <= array[end] && ++small != i) {
                swap(array, small, i);
            } 
        }
        
        swap(array, ++small, end);
        return small;
    }
    
    private void swap(int[] array, int a, int b) {
        int temp = array[a];
        array[a] = array[b];
        array[b] = temp;
    } 
    
　　//验证数组是否合理
    private boolean checkMoreThanHalf (int[] array, int result) {
        int times = 0;
        for (int i = 0; i < array.length; i++) {
            if (array[i] == result)
                times++;
        }
        
        if (times * 2 <= array.length) 
            return false;
        else 
            return true;
    }
}

public class Solution {
    public int MoreThanHalfNum_Solution(int [] array) {
        int len = array.length;
        if (len == 0) return 0;
        if (len == 1) return array[0];
        
        int result = array[0];
        int times = 1;
        
        for (int i = 1; i < len; i++) {
            if (times == 0) {
                result = array[i];
                times = 1;
            }
            else if (array[i] == result) {
                times++;
            }
            else {
                times--;
            }
        }
        
        if (times >= 1 && checkMoreThanHalf(array, result)) 
            return result;
        else 
            return 0;
    }
    
    
    private boolean checkMoreThanHalf (int[] array, int result) {
        int times = 0;
        for (int i = 0; i < array.length; i++) {
            if (array[i] == result)
                times++;
        }
        
        if (times * 2 <= array.length) 
            return false;
        else 
            return true;
    }
}