Insert or Merge（java）

7-13 Insert or Merge（25 分）

According to Wikipedia:

Insertion sort iterates, consuming one input element each repetition, and growing a sorted output list. Each iteration, insertion sort removes one element from the input data, finds the location it belongs within the sorted list, and inserts it there. It repeats until no input elements remain.

Merge sort works as follows: Divide the unsorted list into N sublists, each containing 1 element (a list of 1 element is considered sorted). Then repeatedly merge two adjacent sublists to produce new sorted sublists until there is only 1 sublist remaining.

Now given the initial sequence of integers, together with a sequence which is a result of several iterations of some sorting method, can you tell which sorting method we are using?

Input Specification:

Each input file contains one test case. For each case, the first line gives a positive integer N (≤100). Then in the next line, N integers are given as the initial sequence. The last line contains the partially sorted sequence of the N numbers. It is assumed that the target sequence is always ascending. All the numbers in a line are separated by a space.

Output Specification:

For each test case, print in the first line either "Insertion Sort" or "Merge Sort" to indicate the method used to obtain the partial result. Then run this method for one more iteration and output in the second line the resuling sequence. It is guaranteed that the answer is unique for each test case. All the numbers in a line must be separated by a space, and there must be no extra space at the end of the line.

Sample Input 1:

10
3 1 2 8 7 5 9 4 6 0
1 2 3 7 8 5 9 4 6 0

Sample Output 1:

Insertion Sort
1 2 3 5 7 8 9 4 6 0

Sample Input 2:

10
3 1 2 8 7 5 9 4 0 6
1 3 2 8 5 7 4 9 0 6

Sample Output 2:

Merge Sort
1 2 3 8 4 5 7 9 0 6

思路：

1、是否是插入排序很好判断，前面是有序的，从不有序的那个点开始，后面的元素和初始序列一样。

2、在进行插入排序时，注意应该从前往后判断从哪个点开始不有序的，就从那个点开始排。保证你排完之后，确实有点发生了移动。

 

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.StreamTokenizer;

public class Main {

	public static void main(String[] args) throws IOException {
		// TODO Auto-generated method stub
		StreamTokenizer in = new StreamTokenizer(
				new BufferedReader(new InputStreamReader(System.in)));
		in.nextToken();
		int n = (int) in.nval;
		int a []  = new int[n];
		int b []  = new int [n];
		for(int i =0;i<n;i++) {
			in.nextToken();
			a[i] = (int) in.nval;
		}
		for(int i = 0;i<n;i++) {
			in.nextToken();
			b[i] = (int) in.nval;
		}
		
		boolean bool = judge(a,b,n);
		if(bool) {
			System.out.println("Insertion Sort");
			insert_sort(a,b,n);
		}
		else {
			System.out.println("Merge Sort");
			merge_sort(a,b,n);
		}
		
	}

	private static void merge_sort(int[] a, int[] b, int n) {
		// TODO Auto-generated method stub
		int i;
		int temp [] = new int[n];
		int length=1;
		while(length<n) {
			merge_pass(a,temp,length,n);
			for(i=0;i<n;i++) {
				if(temp[i]!=b[i])
					break;
			}
			if(i==n)
				break;
			
			length*=2;
			
			for(i=0;i<n;i++) {
				temp[i] = a[i];
			}
		}
		length*=2;
		merge_pass(a,temp,length,n);
		
		int flag=0;
		for(i=0;i<n;i++) {
			if(flag!=0)
				System.out.print(" ");
			System.out.print(temp[i]);
			flag =1;
		}
		
	}
	private static void merge_pass(int[] a, int temp[],int length, int n) {
		int i;
		// TODO Auto-generated method stub
		for( i =0;i<=n-2*length;i+=2*length) {
			merge(a,temp,i,i+length,i+2*length-1);
		}
		
		if(n-i>length)
			merge(a,temp,i,i+length,n-1);
		else
			for(int k =i;k<n;k++) {
				temp[k] =a[k];
			}
		
		
	}


	private static void merge(int[] a, int[] temp, int L, int R, int right_end) {
		// TODO Auto-generated method stub
		int left_end =R-1;
		int k =L ;
		int num = right_end-L+1;
		while(L<=left_end&&R<=right_end) {
			if(a[L]<=a[R]) {
				temp[k] = a[L];
				k++;L++;
			}
			else {
				temp[k] = a[R];
				k++;R++;
			}
		}
		
		while(L<=left_end) {
			temp[k] =a[L];
			k++;
			L++;
		}
		
		while(R<=right_end) {
			temp[k] =a[R];
			k++;
			R++;
		}
		
		for(int i =k-1,j =0 ;j<num;j++,i--) {
			a[i] = temp[i];
		}
	}
	private static void insert_sort(int[] a, int[] b, int n) {
		// TODO Auto-generated method stub
		int i,j=0;
		for(i =0;i<n&&b[i]<=b[i+1];i++) {
			;
		}
	
		
		int tmp =a[i+1];
		int flag=0;
		
		for(j =i;j>=0&&b[j]>tmp;j--) {
			b[j+1]=b[j];
			flag=1;
		}
		b[j+1] = tmp;
	
		
		flag=0;
		for(i=0;i<n;i++) {
			if(flag!=0)
				System.out.print(" ");
			System.out.print(b[i]);
			flag =1;
		}
		
	}

	private static boolean judge(int[] a,int[] b, int n) {
		int i;
		// TODO Auto-generated method stub
		for(i = 0;b[i]<=b[i+1]&&i<n-1;i++) {
			;
		}
		
		int flag =0;
		while(flag==0&&i<n-1) {
			if(a[i+1]!=b[i+1]) {
				flag =1;
			}
			i++;
		}
		
		if(flag ==0)
			return true;
		else
			return false;
	}

}