递归与分治思想：治思想 && 折半查找法（迭代 && 递归）

  1 //分治思想：将大问题拆成小问题逐一解决
  2 //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
  3 
  4 //折半查找法（迭代）
  5 #include<stdio.h>
  6 
  7 int search(int str[], int n, int key);
  8 
  9 int main(void)
 10 {
 11     int str[11] = {1,1,2,3,5,8,13,21,34,55,89};
 12     int n,adr;
 13     
 14     printf("请输入你需要查找数据的关键字：");
 15     scanf("%d",&n);
 16     printf("\n");
 17     
 18     adr = search(str,11,n);
 19     if(adr != -1)
 20     {
 21         printf("查找成功，关键字%d所在的位置是：%d\n",n,adr);
 22     }
 23     else
 24     {
 25         printf("查找失败！\n");
 26     }
 27     
 28     return 0;
 29 } 
 30 
 31 int search(int str[], int n, int key)
 32 {
 33     int low,high,mid;
 34     
 35     low = 0;
 36     high = n-1;
 37     mid = (low+high)/2;
 38     
 39     while(low <= high)
 40     {
 41         if(key > str[mid])
 42         {
 43             low = mid+1;
 44             mid = (low+high)/2;
 45         }
 46         if(key < str[mid])
 47         {
 48             high = mid-1;
 49             mid = (low+high)/2;
 50         }
 51         if(key == str[mid])
 52         {
 53             return mid;
 54         }
 55     }
 56     
 57     return -1;
 58 }
 59 
 60 //折半查找法（递归算法）
 61 #include<stdio.h>
 62 
 63 int search(int str[], int low, int high, int key);
 64 
 65 int main(void)
 66 {
 67     int str[11] = {1,1,2,3,5,8,13,21,34,55,89};
 68     int n,addr;
 69     
 70     printf("请输入想要查找的关键字：");
 71     scanf("%d",&n); 
 72     
 73     addr = search(str,0,10,n);  //0是low 10是high 
 74     if(addr == -1)
 75     printf("查找失败！\n");
 76     else
 77     printf("可喜可贺，可口可乐，你查找的关键字 %d 在位置 %d ",n,addr);
 78     
 79     return 0;
 80 } 
 81 
 82 int search(int str[], int low, int high, int key)
 83 {
 84     int mid;
 85     if(low <= high)
 86     {
 87         mid = (low+high)/2;
 88         if(str[mid] == key)
 89         return mid;
 90         else
 91         {
 92             if(key > str[mid])
 93             search(str,mid+1,high,key);
 94             else
 95             search(str,low,mid-1,key);
 96         }
 97     }
 98     else
 99     return -1;
100 }