归并排序MERGE_SORT

MERGE SORT

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1 Merging

    Before looking at the merge sort algorithm to sort n records, let us see how one may merge two  sorted lists to get a single sorted list.

    we'll see two different algorithms for this. The first one is very simple and uses O(n) addtional space.

    //merge two sorted lists, list[p...q] and list[q..r] //to obtain a sorted list sorted[p...r] void merge(int list[], int sorted[], int p, int q, int r) { int i = p; //index for the 1st list, could be deleted just using p int j = q+1; // index for 2nd list int k = p; //index for the sorted list while( i <= q && j <= r ){ if( list[i] <= list[j] ) sorted[k++]= list[i++]; else sorted[k++]= list[j++]; } while( i <= q ) sorted[k++] = list[i++]; while( j <= r ) sorted[k++] = list[j++]; }  

 申请新一内存空间保存从两序列中元素比较的结果，此方法比较简单，时间复杂度为O(n) = O(r-p),对应于两序列长度之和。