求两个排好序的数组合并之后的中位数

来源：互联网发布：窗帘布带的计算法编辑：程序博客网时间：2024/05/15 14:11

void sort(int [], int);

int median(int x[], int y[], int n)
{
     int first_X = 0;        /* lower element of x[]     */
     int first_Y = 0;        /* lower element of y[]     */
     int last_X = n-1;      /* higher element of x[]    */
     int last_Y = n-1;      /* higher element of y[]    */
     int count   = 0;        /* # of smaller items elim. */
     int mid_X, mid_Y;       /* middle element pointers */
     int number;             /* # of elements left       */
     int z[4];               /* working array            */

     while ((last_X - first_X > 1) || (last_Y - first_Y > 1)) {
          mid_X = (first_X + last_X)/2; /* get mid ptrs */
          mid_Y = (first_Y + last_Y)/2;
          if (x[mid_X] <= y[mid_Y]) {
               count   += (mid_X - first_X); /* inc. count*/
               first_X = mid_X; /* elim. lower half x[] */
               last_Y = mid_Y; /* elim. higher half x[] */
          }
          else {
               count   += (mid_Y - first_Y);
               first_Y = mid_Y; /* elim. lower half y[] */
               last_X = mid_X; /* elim. higher half x[] */
          }
     }

     for (number = 0; first_X <= last_X; first_X++)
          z[number++] = x[first_X]; /* collect remainder */
     for ( ; first_Y <= last_Y; first_Y++)
          z[number++] = y[first_Y];

sort(z, number); /* sort them */
return z[n-count-1]; /* pick up appropriate item */
}

/* ------------------------------------------------------ */
/* FUNCTION sort :                                       */
/*    Special routine to sort small arrays with 2, 3 and */
/* 4 elements.                                            */
/* ------------------------------------------------------ */

#define SWAP(x, y) { temp = x; x = y; y = temp; }

void sort(int z[], int n)
{
int temp;

     switch (n) {
          case 4 : if (z[0] >= z[3]) SWAP(z[0], z[3]);
                   if (z[1] >= z[3]) SWAP(z[1], z[3]);
                   if (z[2] >= z[3]) SWAP(z[2], z[3]);
          case 3 : if (z[0] >= z[2]) SWAP(z[0], z[2]);
                   if (z[1] >= z[2]) SWAP(z[1], z[2]);
          case 2 : if (z[0] >= z[1]) SWAP(z[0], z[1]);
     }
}

/* ------------------------------------------------------ */

#include <stdio.h>

void main(void)
{
     int x[] = { 1, 3, 6, 7, 8, 9, 10};
     int y[] = { 2, 4, 5, 11, 12, 13, 14};
     int n   = sizeof(x)/sizeof(int);
     int i;

     printf("\nMedian of Two Sorted Arrays");
     printf("\n===========================");
     printf("\n\nArray #1     Array #2");
     printf( "\n--------     --------");
     for (i = 0; i < n; i++)
          printf("\n%6d%13d", x[i], y[i]);
     printf("\n\nMedian is %d", median(x, y, n));
}