基础算法4——归并排序

import java.util.Random;

public class MergeSort {    
    private double[] bridge;//辅助数组
    
    public void sort(double[] obj){
        if (obj == null){
            throw new NullPointerException("The param can not be null!");
        }
        bridge = new double[obj.length]; // 初始化中间数组
        mergeSort(obj, 0, obj.length - 1); // 归并排序
        bridge = null;
    }
    
    private void mergeSort(double[] obj, int left, int right){
        if (left < right){
            int center = (left + right) / 2;
            mergeSort(obj, left, center);
            mergeSort(obj, center + 1, right);
            merge(obj, left, center, right);
        }
    }
    
    private void merge(double[] obj, int left, 
int center, int right){
        int mid = center + 1;
        int third = left;
        int tmp = left;
        while (left <= center && mid <= right){ 
            // 从两个数组中取出小的放入中间数组
            if (obj[left]-obj[mid]<=10e-6){
                bridge[third++] = obj[left++];
            } else{
                bridge[third++] = obj[mid++];
            }
        }

        // 剩余部分依次置入中间数组
        while (mid <= right){
            bridge[third++] = obj[mid++];
        }
        while (left <= center){
            bridge[third++] = obj[left++];
        }
        // 将中间数组的内容拷贝回原数组
        copy(obj, tmp, right);
    }
    
    private void copy(double[] obj, int left, int right)
    {
        while (left <= right){
            obj[left] = bridge[left];
            left++;
        }
    }
    
    public static void main(String[] args) {
        Random random = new Random(6);

        int arraysize = 10;
        double[] sorted = new double[arraysize];
        System.out.print("Before Sort:");
        for (int j = 0; j < arraysize; j++) {
            sorted[j] = (int) (random.nextDouble() * 100);
            System.out.print((int) sorted[j] + " ");
        }
        System.out.println();

        MergeSort sorter = new MergeSort();
        sorter.sort(sorted);
        
        System.out.print("After Sort:");
        for (int j = 0; j < sorted.length; j++) {
            System.out.print((int) sorted[j] + " ");
        }
        System.out.println();
    }

}