Create merge_sort.cpp

merge/merge_sort.cpp

@@ -0,0 +1,49 @@
+#include<bits/stdc++.h>
+using namespace std;
+#define MAX 2000009
+
+int a[MAX];
+
+void merge(int *a, int p, int q, int r, int& c){
+	int L[q-p+1],R[r-q];
+	for(int i=p;i<=q;i++)	L[i-p]=a[i];
+	for(int i=q+1;i<=r;i++)	R[i-q-1]=a[i];
+
+	int i=0,j=0,k=p;
+	while(i<=(q-p) && j<=(r-q-1)){
+		if(L[i]<=R[j]){
+			a[k]=L[i];
+			k++,i++;
+		}else{
+			c+=q-p-i+1;
+			a[k]=R[j];
+			j++,k++;
+		}
+	}
+	for(;i<=q-p;i++)	a[k++]=L[i];
+	for(;j<=r-q-1;j++)	a[k++]=R[j];
+	return;
+}
+
+void mergeSort(int *a, int p, int r, int& c){
+	if(p<r){
+		int q=(p+r)/2;
+		mergeSort(a,p,q,c);
+		mergeSort(a,q+1,r,c);
+		merge(a,p,q,r,c);
+	}
+	return;
+}
+
+int main(){
+	int n,x;
+	scanf("%d",&n);
+	for(int i=0;i<n;i++)		scanf("%d",&a[i]);
+
+	int c=0;
+	mergeSort(a,0,n-1,c);
+
+	for(int i=0;i<n;i++)    printf("%d ",a[i]);
+// 	printf("\n%d",c);
+	return 0;
+}