c - Sort an array in place according to a sort order defined in another array -

i have array defines sort order array. example, sort array consisting of char * data[] = {"c", "b", "a"};, sort_order array {2, 1, 0} - when array sorted, first element should "c" (which data[sort_order[0]]).

(the background have 2 arrays want sort, second array should use same sort order first one. sort {0, 1, 2} using values first array, , i'd use sort order sort actual values of both arrays.)

the obvious solution create copy of array (new_data), , assign every element correct value defined sort order:

for (int = 0; < n; ++i) {     new_data[i] = data[sort_order[i]]; } 

however, requires making copy of array. there way can swap elements of original array sort them in place without having copy array?

edit: "possible duplicate" use array, precisely trying avoid.

reorder in place, sorts both a[] , i[], rotating "cycles". each store places value in it's proper location, time complexity o(n).

    // reorder in place according sorted indices in     // ta temp value     for(i = 0; < n; i++){         if(i != i[i]){             ta = a[i];             k = i;             while(i != (j = i[k])){                 a[k] = a[j];                 i[k] = k;                 k = j;             }             a[k] = ta;             i[k] = k;         }     } 

i noticed you're using c. in c++, can use lambda compare function compare members of a[], based on indices in i[]. c, can use array of pointers p[] instead of array of indices i[].

    /* create array of pointers a[] */     for(i = 0; < n; i++)         p[i] = &a[i];     /* sort array of pointers, compare custom compare function */     qsort(p, n, sizeof(p[0]), compare);     /* reorder a[] according array of pointers */     for(i = 0; < n; i++){         if(i != p[i]-a){             ta = a[i];             k = i;             while(i != (j = p[k]-a)){                 a[k] = a[j];                 p[k] = &a[k];                 k = j;             }             a[k] = ta;             p[k] = &a[k];         }     } 

example custom compare qsort() if a[] contains integers. since qsort() passes pointers p[] parameters compare(), , since p[] array of pointers, passed parameters compare() pointers pointers.

int compare(const void *pp0, const void *pp1) {     return( (**(int **)pp0) - (**(int **)pp1) ); } 

if goal sort second array b[], based on sorting a[], add lines like:

        /* ... after ta = a[i] */         tb = b[i];             /* ... after a[k] = a[j] */             b[k] = b[j];         /* ... after a[k] = ta */         b[k] = tb;