Sort--mergesort Merge sort?

　　MergeSort ' s Implementation

The central idea of mergetsort is to divide and conquer ideas and solve big problems by solving every small problem.

Let's say you have 2 sorted arrays

arrays [4] [8] and array [5] [7] are sorted

4 is the smallest value of the first array and the second array with the smallest value 5 to compare 4 < 5 so the smallest element is 4

After the first element is finished [4] [NULL] [NULL] [NULL]

Then the second element, 8 and 5, is compared. 5 relatively small

So it is [4] [5] [NULL] [NULL], then the first array with the smallest value of 8 and the second array is the best value of 7 compared. 7 < 8

So it becomes [4] [5] [7] [8].

So the key to the problem is to first sort the 2 arrays separately. and merge into a large array. Steal a picture of others below. Quack Gaga

　　　　

The complexity of MergeSort is NLGN. Pretty fast algorithm. And it's stable.

Here is a concrete implementation

　　

    //time:n log (N) & wasting space that proportional to N     Public Static voidsort (comparable[] a) {sort (A,NewComparable[a.length], 0, a.length-1); }        //The mid is already in order,//This is the merge method .//the length of a and auxiliary arrays need to be consistent    /**I J * [ ] [] [] [] [] * Low mid hi*/    Private Static voidSort (comparable[] A, comparable[] aux,intLowinthi) {        if(Low >= hi)return; intMiddle = low + (Hi-low)/2; Sort (A, aux, low, middle); //Sort LeftSort (A, aux, middle + 1, HI);//Sort Rightmerge (A, aux, Low, middle, hi); }        /**I j * [] [] [] [] [ ] * Low mid hi */    Private Static voidMerge (comparable[] A, comparable[] aux,intLowintMiddle,inthi) {        inti =Low ; intj = Middle + 1;  for(intK = low; K <= Hi; k++) Aux[k]= A[k];//copy elements to a secondary array                 for(intK = low; K <= Hi; k++) {                        //the first 2 judging conditions must be in front. //Otherwise, there will be a null pointer exception when comparing//because it's possible that J has gone beyond the size of hi.            if(i > middle) a[k] = aux[j++]; Else if(J > Hi) a[k] = aux[i++]; Else if(Less (aux[i],aux[j])) a[k] = aux[i++];//            ElseA[k] = aux[j++]; }    }

Merge Sort

Https://github.com/Cheemion/algorithms/blob/master/src/com/algorithms/sort/MergeSort.java

Sort--mergesort Merge sort?