在 C 中排序后跟踪数组的原始索引 [英] keeping track of the original indices of an array after sorting in C

问题描述

我有一个数组，比如 A[5]，这 5 个元素是 5,4,1,2,3.现在我按升序对这些数组进行排序.所以结果数组现在将是 1,2,3,4,5.我使用 stdlib.h 的 qsort() 函数对此进行排序.问题是如何获得原始数组相对于我的新数组的索引.最初我的索引是 0,1,2,3,4 对应的 5,4,1,2,3 值，现在索引已更改为 2,3,4,1,0.如何在 C 中有效地获得这些索引?在此先感谢您(如果可能，请编写代码)

I have an array let's say A[5], the 5 elements are 5,4,1,2,3. Now I sort these arrays in ascending order. so the resulting array will now be 1,2,3,4,5. I use qsort() function of stdlib.h to sort this. The question is how can I get the indices of the original array with respect to my new array. originally my indices were 0,1,2,3,4 for corresponding values of 5,4,1,2,3 and now the indices have changed to 2,3,4,1,0. How can I get these indices efficiently in C? Thank you in advance(please write the code if possible)

推荐答案

在限定条件下还有如下方法.

There is also a method as follows under limited conditions.

#include <stdio.h>

int main(void){
    int data[] ={ 5,4,1,2,3 }; //Without duplication, The number of limited range.
    int size = sizeof(data)/sizeof(*data);
    int keys[size];
    int i;

    printf("data :\n");
    for(i=0;i<size;i++){
        printf("%d ",data[i]);
    }
    for(i=0;i<size;i++){
        keys[data[i]-1]=i;
    }

    printf("\n\ndata\tindex\n");
    for(i=0;i<size;i++){
        printf("%d\t%d\n", data[keys[i]], keys[i]);
    }
    return 0;
}
/* result sample
data :
5 4 1 2 3

data    index
1       2
2       3
3       4
4       1
5       0
*/

<小时>

如建议的那样对索引数组@Kerrek 进行排序.

---

How to sort an array of index @Kerrek is as proposed.

#include <stdio.h>
#include <stdlib.h>

int *array;

int cmp(const void *a, const void *b){
    int ia = *(int *)a;
    int ib = *(int *)b;
    return array[ia] < array[ib] ? -1 : array[ia] > array[ib];
}

int main(void){
    int data[] ={ 5,4,1,2,3 };
    int size = sizeof(data)/sizeof(*data);
    int index[size];//use malloc to large size array
    int i;

    for(i=0;i<size;i++){
        index[i] = i;
    }
    array = data;
    qsort(index, size, sizeof(*index), cmp);
    printf("\n\ndata\tindex\n");
    for(i=0;i<size;i++){
        printf("%d\t%d\n", data[index[i]], index[i]);
    }
    return 0;
}

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