Sort algorithm two: merge sort

Merge sort is used to divide and conquer thought, namely divide-cure-three steps, the average time complexity of the algorithm is O (NLGN).

(i) Algorithm implementation

1 Private voidMerge_sort (int[] Array,intFirstintLast ) {2         if(First + 1 <Last ) {3             intMid = (first + last)/2;4 Merge_sort (Array, first, mid);5 Merge_sort (Array, Mid, last);6 7             //Merge8             inti =First ;9             intj =mid;Ten             int[] Temparray =New int[Last-First ]; One              for(intk = 0; K < Temparray.length; k++) { A                 if(J = =Last ) { -Temparray[k] = array[i++]; -}Else if(i = =mid) { theTemparray[k] = array[j++]; -}Else if(Array[i] <Array[j]) { -Temparray[k] = array[i++]; -}Else if(Array[i] >=Array[j]) { +Temparray[k] = array[j++]; -}Else { +                     Throw NewRuntimeException ("Merge sort error.")); A                 } at             } -System.arraycopy (temparray, 0, array, first, last-First ); -         } -}

Merge Sort

1) The algorithm is not sorted in situ and requires additional space when merging

2) The average time complexity of the algorithm is O (NLGN)

(ii) Simulation results

**************************************************
Number to Sort is:2500
Array to sort is:{633649,71377,977368,56277,635475,755791,746668,373470,820128,669757 ...}
Cost time of "Mergsort" is (milliseconds): 1
Sort result of "Mergsort": {695,711,935,1074,1571,1681,2434,3967,4104,4452 ...}
**************************************************
Number to Sort is:25000
Array to sort is:{62806,677129,876202,279782,662046,978299,979879,374196,303999,484652 ...}
Cost time of "Mergsort" is (milliseconds): 5
Sort result of "Mergsort": {15,34,74,94,131,141,316,372,375,417 ...}
**************************************************
Number to Sort is:250000

Array to sort is:{617507,750026,202102,267444,690991,638097,868240,413838,774218,463780 ...}

Cost time of "Mergsort" is (milliseconds): 67
Sort result of "Mergsort": {6,9,19,28,31,39,44,45,56,59 ...}

Related code:

1  PackageCom.cnblogs.riyueshiwang.sort;2 3 Importjava.util.Arrays;4 5  Public classMergeSortextendsAbstractsort {6 7 @Override8     protected voidSortint[] tosort) {9Merge_sort (tosort, 0, tosort.length);Ten     } One  A     Private voidMerge_sort (int[] Array,intFirstintLast ) { -         if(First + 1 <Last ) { -             intMid = (first + last)/2; the Merge_sort (Array, first, mid); - Merge_sort (Array, Mid, last); -  -             //Merge +             inti =First ; -             intj =mid; +             int[] Temparray =New int[Last-First ]; A              for(intk = 0; K < Temparray.length; k++) { at                 if(J = =Last ) { -Temparray[k] = array[i++]; -}Else if(i = =mid) { -Temparray[k] = array[j++]; -}Else if(Array[i] <Array[j]) { -Temparray[k] = array[i++]; in}Else if(Array[i] >=Array[j]) { -Temparray[k] = array[j++]; to}Else { +                     Throw NewRuntimeException ("Merge sort error.")); -                 } the             } *System.arraycopy (temparray, 0, array, first, last-First ); $         }Panax Notoginseng     } -  the      Public Static voidMain (string[] args) { +          for(intj = 0, n = 2500; J < 3; j + +, n = n * 10) { A System.out the. println ("**************************************************"); +System.out.println ("Number to Sort is:" +n); -             int[] array = Commonutils.getrandomintarray (n, 1000000); $System.out.print ("Array to sort is:"); $ Commonutils.printintarray (array); -  -             int[] Array1 =arrays.copyof (array, n); the             Newmergesort (). Sortandprint (array1); -         }Wuyi     } the}

Mergesort.java

Sort algorithm two: merge sort