練習3.1

折半查找

 

 

代碼：

 

#include <stdio.h>
#include <time.h>
#include <stdlib.h>
#define ARRAY_LEN 20
int binsearch(int x, int v[], size_t b, size_t e);
void sort(int v[], size_t b, size_t e);

int main(int argc, char *argv[])
{
    int arr[ARRAY_LEN];
    srand((int)time(NULL));
    for (int i = 0; i != ARRAY_LEN; ++i)
        arr[i] = 0 + rand() % 15;
    sort(arr, 0, ARRAY_LEN);
    for (int i = 0; i != ARRAY_LEN; ++i)
        printf("%d ", arr[i]);

    printf("\nfind 10 at index: %d\n", binsearch(10, arr, 0, ARRAY_LEN));
    return 0;
}

int binsearch(int x, int v[], size_t b, size_t e)
{
    int low = b;
    int high = e - 1;
    int mid = (low + high) / 2;
    while (low <= high && v[mid] != x) {
        if (x < v[mid])
            high = mid - 1;
        else
            low = mid + 1;
        mid = (low + high) / 2;
    }

    if (v[mid] == x)
        return mid;
    else
        return -1;
}
void sort(int v[], size_t b, size_t e)
{
    for (size_t i = b; i != e; ++i) {

        for (size_t j1 = i+1; j1 != e; ++j1) {
            if (v[j1] < v[i]) {
                int item = v[j1];
                v[j1] = v[i];
                v[i] = item;
            }
        }
    }
}