[英]Weird bug in mergesort
I've just programmed the following simple merge function in mergesort which follows exactly the one written in CLRS book. 我刚刚在mergesort中编写了以下简单的合并功能,该功能完全遵循CLRS书中编写的功能。
#include<iostream>
#include<vector>
#include<limits>
using namespace std;
//Define the numerical positive infinity
const int INFP = numeric_limits<int>::max();
void MERGE(vector<int> A, int p, int q, int r){
//Create the size of left and right array
int n1 = q-p+1;
int n2 = r-q;
//Create the left array
vector<int> L(n1+1);
for(int i=0; i<n1;i++){
L[i] = A[i];
}
L[n1] = INFP; //Insert sentinel here!
//Create the right array
vector<int> R(n2+1);
for(int i=0; i<n2;i++){
R[i] = A[q+i+1];
}
L[n2] = INFP; //Insert sentinel here!
int i = 0;
int j = 0;
for(int k = 0; k <= r; k++){
if(L[i]<=R[j]){
A[k] = L[i];
i=i+1;
}
else{
A[k] = R[j];
j=j+1;
}
}
for(int m=0;m<4;m++){
cout<< A[m] << " ";
}
cout << endl;
}
int main(){
//test for merge function:
vector<int> A(4);
A[0]=1;
A[1]=3;
A[2]=2;
A[3]=4;
MERGE(A,0,1,3);
for(int m=0;m<4;m++){
cout<< A[m] << " ";
}
cout << endl;
return 0;
}
However, it gave me the following print out, which really confused me: 但是,它给了我以下打印输出,这确实让我感到困惑:
1 2 3 4
1 3 2 4
I don't know if it's the problem of the void function that I can't use void function for vectors or something else. 我不知道我是否不能将void函数用于矢量或其他问题,这是void函数的问题。
Really hope someone can help me out. 真的希望有人能帮助我。 Thanks!
谢谢!
It's because you pass the vector by value , meaning you modify a local copy. 这是因为您通过值传递向量,这意味着您修改了本地副本。 Pass it by reference instead.
而是通过引用传递它。
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