反转计数给出错误的输出
Inversion Count gives wrong output
以下程序用于计算数组中的反转编号。它给了我错误的输出,无法调试代码?对于输入数组:arr[]= { 3,1,2 } 输出 : 3但是对于排序的输入数组,它给出了正确的答案?
#include <iostream>
using namespace std;
int merge_inversion( unsigned long long int* A, long int l, long int m,
long int r ){
int i= l, j= m;
int inv_count= 0;
while( i <= m-1 && j <= r ){
if( A[i] <= A[j] ){
i++;
}else{
j++;
inv_count+= m-i;
}
}
return inv_count;
}
unsigned long long int inversion_count( unsigned long long int* A, long
int start, long int end ){
int mid, inv_count= 0;
if( start < end ){
mid= (start + end)/2;
inv_count= inversion_count( A, start, mid );
inv_count+= inversion_count( A, mid+1, end );
inv_count+= merge_inversion( A, start, mid+1, end );
}
return inv_count;
}
int main(){
long int T;
cin >> T;
while( T-- ){
cout << endl;
long int N;
cin >> N;
unsigned long long int *arr= new unsigned long long int[N];
for( int i=0; i<N; i++ )
cin >> arr[i];
cout << inversion_count( arr, 0, N-1 );
cout << endl;
}
}
问题出在代码的这一部分:
while( i <= m-1 && j <= r ){
if( A[i] <= A[j] ){ //You only count the inversions, but forgot to sort the array.
i++;
}else{
j++;
inv_count+= m-i;
}
}
对于排序问题,我们应该创建一个临时数组来存储临时排序结果。
这是一个有效的程序。和你的相似。
#include <iostream>
using namespace std;
int g_nCount;
void mergearray(unsigned long long int* a, int first, int mid, int last, unsigned long long int* temp)
{
int i = first, j = mid + 1;
int m = mid, n = last;
int k = 0;
while (i <= m && j <= n)
{
if (a[i] < a[j])
temp[k++] = a[i++]; //Sorting and counting
else
{
temp[k++] = a[j++];
g_nCount += m - i + 1;
}
}
while (i <= m)
temp[k++] = a[i++];
while (j <= n)
temp[k++] = a[j++];
for (i = 0; i < k; i++) //Save sorting result to the orginal array.
a[first + i] = temp[i];
}
void mergesort(unsigned long long int* a, int first, int last, unsigned long long int* temp)
{
if (first < last)
{
int mid = (first + last) / 2;
mergesort(a, first, mid, temp); //Left
mergesort(a, mid + 1, last, temp); //Right
mergearray(a, first, mid, last, temp); //Merge
}
}
bool MergeSort(unsigned long long int* a, int n)
{
unsigned long long int *p = new unsigned long long int[n];
if (p == NULL)
return false;
mergesort(a, 0, n - 1, p);
return true;
}
int main(){
long int T;
cin >> T;
while( T-- ){
cout << endl;
long int N;
cin >> N;
unsigned long long int *arr= new unsigned long long int[N];
for( int i=0; i<N; i++ )
cin >> arr[i];
g_nCount = 0;
MergeSort(arr, N);
cout << g_nCount << endl;
}
}
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