描述
Given two sorted integer arrays A and B, merge B into A as one sorted array.
Note: You may assume that A has enough space to hold additional elements from B. The number of
elements initialized in A and B are m and n respectively.
代码
package sort; public class MergeSortedArray { public static void main(String[] args) { // TODO Auto-generated method stub // 这道题是说让B merge到 A 里面。 int[] A = { 1, 14, 15, 19 }; int m=4; int n=6; int[] B = { 2, 3, 17, 20, 34, 67 }; int[] C = mergeTwoList(A, B); for (int k : C) { System.out.println(k); } ListNode left = new ListNode(1); // head.add(1); left.add(3); left.add(7); left.add(11); left.add(13); left.add(15); left.print(); System.out.println(); ListNode right = new ListNode(2); // head.add(1); right.add(4); right.add(6); right.add(8); right.add(10); right.add(16); right.print(); System.out.println(); ListNode clistnode = mergeTwoList(left, right); clistnode.print(); merge(A,m,B,n); for(int p:A) { System.out.println(p); } } public static int[] mergeTwoList(int[] A, int[] B) { int[] C = new int[A.length + B.length]; int k = 0; int i = 0; int j = 0; while (i < A.length && j < B.length) { if (A[i] < B[j]) C[k++] = A[i++]; else C[k++] = B[j++]; } while (i < A.length) { C[k++] = A[i++]; } while (j < B.length) { C[k++] = B[j++]; } return C; } public static ListNode mergeTwoList(ListNode leftlist,ListNode rightlist) { if(rightlist==null) { return leftlist; } if(leftlist==null) { return rightlist; } ListNode fakehead=new ListNode(-1); ListNode ptr=fakehead; while(rightlist!=null&&leftlist!=null) { if(rightlist.data<leftlist.data) { ptr.next=rightlist; ptr=ptr.next; rightlist=rightlist.next; }else { ptr.next=leftlist; ptr=ptr.next; leftlist=leftlist.next; } } if(rightlist!=null) { ptr.next=rightlist; } if(leftlist!=null) { ptr.next=leftlist; } return fakehead.next; } // 这道题是不能借助一个新的array的,那么我们就不好从前往后比了(不好插入位置)。 // 方便的方法是从后往前比,然后最后处理剩下的元素。 public static void merge(int[] A,int m,int[] B,int n) { while(m>0&&n>0) { if(A[m-1]>B[n-1]) { A[m+n-1]=A[m-1]; m--; }else { A[m+n-1]=B[n-1]; n--; } } while(n>0) { A[m+n-1]=B[n-1]; n--; } } }
归并排序算法
将待排序序列R[0...n-1]看成是n个长度为1的有序序列,将相邻的有序表成对归并,得到n/2个长度为2的有序表;将这些有序序列再次归并,得到n/4个长度为4的有序序列;如此反复进行下去,最后得到一个长度为n的有序序列。
综上可知:
归并排序其实要做两件事:
(1)“分解”——将序列每次折半划分
(2)“合并”——将划分后的序列段两两合并后排序
package sort; public class MergeSort { public static void main(String[] args) { // TODO Auto-generated method stub int[] array = { 9, 1, 5, 3, 4, 2, 6, 8, 7 }; MergeSort merge = new MergeSort(); System.out.print("排序前: "); merge.printAll(array); merge.sort(array); System.out.print("排序后: "); merge.printAll(array); } public void Merge(int[] array, int low, int mid, int high) { int i = low; // i是第一段序列的下标 int j = mid + 1; // j是第二段序列的下标 int k = 0; // k是临时存放合并序列的下标 int[] array2 = new int[high - low + 1]; // array2是临时合并序列 // 扫描第一段和第二段序列,直到有一个扫描结束 while (i <= mid && j <= high) { // 判断第一段和第二段取出的数哪个更小,将其存入合并序列,并继续向下扫描 if (array[i] <= array[j]) { array2[k] = array[i]; i++; k++; } else { array2[k] = array[j]; j++; k++; } } // 若第一段序列还没扫描完,将其全部复制到合并序列 while (i <= mid) { array2[k] = array[i]; i++; k++; } // 若第二段序列还没扫描完,将其全部复制到合并序列 while (j <= high) { array2[k] = array[j]; j++; k++; } // 将合并序列复制到原始序列中 for (k = 0, i = low; i <= high; i++, k++) { array[i] = array2[k]; } } public void MergePass(int[] array, int gap, int length) { int i = 0; // 归并gap长度的两个相邻子表 for (i = 0; i + 2 * gap - 1 < length; i = i + 2 * gap) { Merge(array, i, i + gap - 1, i + 2 * gap - 1); } // 余下两个子表,后者长度小于gap if (i + gap - 1 < length) { Merge(array, i, i + gap - 1, length - 1); } } public int[] sort(int[] list) { for (int gap = 1; gap < list.length; gap = 2 * gap) { MergePass(list, gap, list.length); System.out.print("gap = " + gap + ": "); this.printAll(list); } return list; } public void printAll(int[] list) { for (int value : list) { System.out.print(value + " "); } System.out.println(); } }