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carrayscomplexity-theoryarray-algorithms

Double dimension array sorting in O(n) time

I was asked a question in interview for sorting a double dimension array in O(n) time.How is it possible to do it in O(n).Can someone shed some light on it.. Thank you.

Input:

3 5 7 1
4 9 2 0
9 3 6 2

Output

0 1 2 2 
3 3 4 5  
6 7 9 9
Solution

  • You can sort as a plain array.
    E.g.

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


int cmp(const void *a, const void *b){
    return *(int*)a - *(int*)b;
}

#define ROW_SIZE 3
#define COL_SIZE 4

int main(void){
    int M[ROW_SIZE][COL_SIZE]={{3,5,7,1},{4,9,2,0},{9,3,6,2}};
    int c,r,*p;

    for(p=&M[0][0],r=0;r<ROW_SIZE;++r){
        for(c=0;c<COL_SIZE;++c){
            printf("%d ",*p++);
        }
        printf("\n");
    }
    printf("\n");
    qsort(&M[0][0], ROW_SIZE*COL_SIZE, sizeof(int), cmp);
    for(p=&M[0][0],r=0;r<ROW_SIZE;++r){
        for(c=0;c<COL_SIZE;++c){
            printf("%d ",*p++);
        }
        printf("\n");
    }

    return 0;
}