/* file name: binarySearch.c */
/* 二元搜尋 */

#include <stdio.h>
#include <stdlib.h>
int main()
{
    int data[10] = {12, 23, 29, 38, 44, 57, 64, 75, 82, 98};
    int i, left = 0, right = 9, mid, cnt = 0, input, ok = 0;
    printf("\n<< Binary search >>\n");
    printf("\n已排序好的資料: ");
    for(i = 0; i < 10; i++)
        printf("%d  ", data[i]);
    printf("\n");
    
    printf("\n請輸入欲找尋的資料: ");
    scanf("%d", &input);
    printf("\nSearching....\n");
    mid = (left + right)/2;     /* 鍵值在第M筆 */
    while (left <= right && ok == 0) {
        printf("\n第%2d 次找的資料是: %d!", ++cnt, data[mid]);
        /* 欲搜尋的資料小於鍵值，則資料在鍵值的前面 */
        if(data[mid] > input) {
            right = mid - 1;
            printf("\n ---> 要找的資料小於 %d\n", data[mid]);
        }
        /* 否則資料在鍵值的後面 */
        else {
            if(data[mid] < input) {
                left = mid + 1;
                printf("\n ---> 要找的資料大於 %d\n", data[mid]);
            }
            else {
                printf("\n\n找到了, %d 是在索引 %d 的位置!\n", input, mid);
                ok = 1;
            }
        }
        mid = (left + right)/2;
    }
    
    if(ok == 0)
        printf("\n\n抱歉, %d 找不到!", input);
    printf("\n");

    return 0;
}