1. The document describes the merge sort algorithm for sorting an array of integers in C code. 2. It works by recursively dividing the array into single element subarrays, and then merging the subarrays back together in a sorted order. 3. The key steps are recursively calling the mergesort function to divide the array, and calling the merge function to merge the divided subarrays back together in sorted order.

1. MERGE SORT UNDERSTANDING CODE in C By-MohitTare mohittare@yahoo.com

2. MERGE SORT – understanding code #include<stdio.h> intmergesort(int*,int,int); void merge(int*,int,int,int); int main() { int a[5]={3,5,2,6,8}; inti; mergesort(a,0,4); for(i=0;i<5;i++) printf("%d",a[i]); return 0; } 3 5 2 6 8

3. intmergesort(inta[], int low, int high) { 0,4 int mid; if(low<high) { mid=(low+high)/2;(2) mergesort(a,low,mid);(a,0,2) mergesort(a,mid+1,high); merge(a,low,high,mid); } return(0); } intmergesort(int a[], int low, int high) { 0,0 int mid; if(low<high)(0<0-false) { mid=(low+high)/2; mergesort(a,low,mid); mergesort(a,mid+1,high); merge(a,low,high,mid); } return(0);(now return will give control to Nearest function call) } intmergesort(int a[], int low, int high) { 0,2 int mid; if(low<high) { mid=(low+high)/2;(1) mergesort(a,low,mid);(0,1) mergesort(a,mid+1,high); merge(a,low,high,mid); } return(0); } intmergesort(int a[], int low, int high) { 0,1 int mid; if(low<high) { mid=(low+high)/2;(0) mergesort(a,low,mid);(0,0) mergesort(a,mid+1,high); merge(a,low,high,mid); } return(0); }

4. intmergesort(inta[], int low, int high) { 0,1 int mid; if(low<high) { mid=(low+high)/2;(0) mergesort(a,low,mid); mergesort(a,mid+1,high); merge(a,low,high,mid); } 0,1,0 return(0); } intmergesort(int a[], int low, int high) { 0,0 int mid; if(low<high)(0<0-false) { mid=(low+high)/2; mergesort(a,low,mid); mergesort(a,mid+1,high); merge(a,low,high,mid); } return(0); } intmergesort(int a[], int low, int high) { (1,1) int mid; if(low<high)(1<1-false) { mid=(low+high)/2; mergesort(a,low,mid); mergesort(a,mid+1,high); merge(a,low,high,mid); } return(0); } intmergesort(int a[], int low, int high) { 0,1 int mid; if(low<high) { mid=(low+high)/2;(0) mergesort(a,low,mid);(0,0) mergesort(a,mid+1,high);(0+1,1) merge(a,low,high,mid); } return(0); }

5. Until now array has been divided into 1 element each. Now array is merged and sorted in the merge function

6. void merge(int a[], int low, int high, int mid) { 0,1,0 int b[20],l1,r1,i; l1=low;0 r1=mid+1;1 l1 r1 i i=low;0 while((l1<=mid) && (r1<=high)) { 0<=0 1<=1 if(a[l1]<a[r1]) { 3<5 b[i]=a[l1];b[0]=3 l1=l1+1;l1=1 i=i+1;i1=1 } else { b[i]=a[r1]; r1=r1+1; i=i+1; } } while(l1<=mid)1<=0 { b[i]=a[l1]; l1=l1+1; i=i+1; } while(r1<=high)1<=1 { b[i]=a[r1];b[1]=5 r1=r1+1;r1=2 i=i+1;i=2 } For(j=low;j<i;j++) a[j]=b[j]; } 3 3 5 2 6 8 1. 3 5 3 5 2 6 8 i 3 5

7. |----------------------; |----------------------; while(r1<=high) { b[i]=a[r1]; r1=r1+1; i=i+1; } It will transfer the current values of b array to a array for(j=low;j<i ;j++) { a[j]=b[j]; } }

8. IN next recursive pass or call to merge 3 5 3 5 2 6 8 void merge(int a[], int low, int high, int mid) { 0,2,1 int b[20],l1,r1,i; l1=low;0 r1=mid+1;2 l1 r1 i=low;0 while((l1<=mid) && (r1<=high)) { 0<=1 2<=2 if(a[l1]<a[r1]) { 3<2 b[i]=a[l1]; l1=l1+1; l1 i=i+1; } else { b[i]=a[r1];b[0]=2 r1=r1+1;r1=3 i=i+1;i=1 } } while(l1<=mid)0<=1 { b[i]=a[l1];b1=3 l1=l1+1;l1=1 i=i+1;i=2 } while(r1<=high)3<=2 { b[i]=a[r1]; r1=r1+1; i=i+1; } for(j=low;j<i;j++) a[j]=b[j]; } 3 5 3 5 2 6 8 3 5 2 6 8 2 5 r1 3 5 2 6 8 2 3 3 5 2 6 8 2 3 5

9. IN next recursive pass or call to merge 2 3 5 2 3 5 6 8 void merge(int a[], int low, int high, int mid) { a,3,4,3 int b[20],l1,r1,i; l1=low;l1=3 r1=mid+1;r1=4 i=low;i=3 while((l1<=mid) && (r1<=high)) { 3<=3 4<=4 if(a[l1]<a[r1]) { b[i]=a[l1];b[3]=6 l1=l1+1;l1=4 i=i+1;i1=4 } else { b[i]=a[r1]; r1=r1+1; i=i+1; } } while(l1<=mid) { b[i]=a[l1]; l1=l1+1; i=i+1; } while(r1<=high)4<=4 { b[i]=a[r1];b[4]=8 r1=r1+1;r1=5 i=i+1;i=5 } For(j=low;j<i;j++) a[j]=b[j]; } 2 3 5 6 8 2 3 5 2 3 5 6 2 3 5 6 8 2 3 5 6 8

10. IN LAST recursive pass or call to merge 2 3 5 6 8 2 3 5 6 8 void merge(int a[], int low, int high, int mid) { 0,4,2 int b[20],l1,r1,i; l1=low;l1=0 r1=mid+1;r1=3 i=low;i=0 while((l1<=mid) && (r1<=high)) { 0<=2 3<=4 if(a[l1]<a[r1]) { 2<6 b[i]=a[l1];b[0]=2 l1=l1+1;l1=1 i=i+1;i=1 } else { b[i]=a[r1]; r1=r1+1; i=i+1; } } while(l1<=mid) { b[i]=a[l1]; l1=l1+1; i=i+1; } while(r1<=high)3<=4 { b[i]=a[r1];b[3]=6 r1=r1+1;r1=4 i=i+1;i=4 } For(j=low;j<i;j++ a[j]=b[j]; } 2 3 5 6 8 2 3 5 6 8 2 3 5 6 8 2 3 5 6 8 2 3 5 6 8 2 3 5 6 8 2 3 5 6 8 2 3 5 6 8 2 3 5 6 8 2 3 5 6 8

11. FINALLY SORTED ARRAY 2 3 5 6 8

12. THANK YOU!