递归与分治思想：治思想 && 折半查找法（迭代 && 递归）

//分治思想：将大问题拆成小问题逐一解决
//折半查找法：不断缩小一半查找的范围，知道达到目的，效率较高。  详情见：https://fishc.com.cn/thread-27964-1-1.html

//折半查找法（迭代）
#include<stdio.h>

int search(int str[], int n, int key);

int main(void)
{
    int str[11] = {1,1,2,3,5,8,13,21,34,55,89};
    int n,adr;
    
    printf("请输入你需要查找数据的关键字：");
    scanf("%d",&n);
    printf("\n");
    
    adr = search(str,11,n);
    if(adr != -1)
    {
        printf("查找成功，关键字%d所在的位置是：%d\n",n,adr);
    }
    else
    {
        printf("查找失败！\n");
    }
    
    return 0;
} 

int search(int str[], int n, int key)
{
    int low,high,mid;
    
    low = 0;
    high = n-1;
    mid = (low+high)/2;
    
    while(low <= high)
    {
        if(key > str[mid])
        {
            low = mid+1;
            mid = (low+high)/2;
        }
        if(key < str[mid])
        {
            high = mid-1;
            mid = (low+high)/2;
        }
        if(key == str[mid])
        {
            return mid;
        }
    }
    
    return -1;
}

//折半查找法（递归算法）
#include<stdio.h>

int search(int str[], int low, int high, int key);

int main(void)
{
    int str[11] = {1,1,2,3,5,8,13,21,34,55,89};
    int n,addr;
    
    printf("请输入想要查找的关键字：");
    scanf("%d",&n); 
    
    addr = search(str,0,10,n);  //0是low 10是high 
    if(addr == -1)
    printf("查找失败！\n");
    else
    printf("可喜可贺，可口可乐，你查找的关键字 %d 在位置 %d ",n,addr);
    
    return 0;
} 

int search(int str[], int low, int high, int key)
{
    int mid;
    if(low <= high)
    {
        mid = (low+high)/2;
        if(str[mid] == key)
        return mid;
        else
        {
            if(key > str[mid])
            search(str,mid+1,high,key);
            else
            search(str,low,mid-1,key);
        }
    }
    else
    return -1;
}