歸併排序算法

歸併排序算法的時間複雜度爲O(NlogN)

合併排序算法就是把多個有序數據表合併成一個有序數據表。若是參與合併的只有兩個有序表，則稱爲二路合併。

/**
 * Created by Administrator on 2018-04-05.
 */
public class Merge {
    static final int SIZE = 15;
    static void mergeOne(int a[],int b[],int n,int len) {
        int i,j,k,s,e;
        s = 0;
        while (s + len < n) {
            e = s + 2 * len - 1;
            if (e >= n) {
                e = n - 1;
            }
            k = s;
            i = s;
            j = s + len;
            while (i < s + len && j <= e) {
                if (a[i] <= a[j]) {
                    b[k++] = a[i++];
                }else {
                    b[k++] = a[j++];
                }
            }
            while (i < s + len) {
                b[k++] = a[i++];
            }
            while (j <= e) {
                b[k++] = a[j++];
            }
            s = e + 1;
        }
        if (s < n) {
            for (;s < n;s++) {
                b[s] = a[s];
            }
        }
    }
    static void mergeSort(int a[],int n) {
        int h,count,len,f;
        count = 0;
        len = 1;
        f = 0;
        int[] p = new int[n];
        while (len < n) {
            if (f == 1) {
                mergeOne(p,a,n,len);
            }else {
                mergeOne(a,p,n,len);
            }
            len = len * 2;
            f = 1 - f;
            count++;
            System.out.printf("第" + count + "步排序結果:");
            for (h = 0;h < SIZE;h++) {
                System.out.printf(" " + a[h]);
            }
            System.out.printf("\n");
            if (f == 1) {
                for (h = 0;h < n;h++) {
                    a[h]  = p[h];
                }
            }
        }
    }
    public static void main(String[] args) {
        int[] shuzu = new int[SIZE];
        int i;
        for (i = 0;i < SIZE;i++) {
            shuzu[i] = (int)(100 + Math.random() * (100 + 1));
        }
        System.out.print("排序前的數組爲:\n");
        for (i = 0;i < SIZE;i++) {
            System.out.print(shuzu[i] + " ");
        }
        System.out.print("\n");
        mergeSort(shuzu,SIZE);
        System.out.print("排序後的數組爲:\n");
        for (i = 0;i < SIZE;i++) {
            System.out.print(shuzu[i] + " ");
        }
        System.out.print("\n");
}
}