查找算法（分割查找）

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

//顺序表查找
//从头到尾逐个比较，找到就返回下标，找不到返回0
//时间复杂度O(n)
int Sequential_Search(int *array, int len, int key){
    int i;
    array[0] = key;
    i = len;
    while(array[i] != key){
        i--;
    }
    return i;
}
void Sequential_Sear(){
    int arr[] = {0,3,2,6,5,3,7,8,1}; //注意0号元素不放实际数据，用来存放key
    int key = 70;

    int get = Sequential_Search(arr,8,key); //顺序查找
    printf(" key is in %d  ",get);

}
//end

//折半查找（二分查找）
//先对要查找的线性表排序，然后取中间记录比较，不符合就在中间到头（或尾）的一半查找，每次取查找区域的中间位置
//时间复杂度O(log n)
//由于折半查找的前提条件需要有序表顺序存储，对于静态查找表，一次排序后不再变化，这样的算法已经比较好了。
//但对于需要频繁执行插入或删除操作的数据集来说，维护有序的排序会带来不小的工作量，就不建议使用
int Binary_Search(int *array, int len, int key){
    
    int low,high,middle;
    low = 0;
    high = len-1;
    while(low <= high){
        
        //middle = (low+high)/2;
        middle = low + (high - low) * (key - array[low]) / (array[high] - array[low]);
        if(key < array[middle]){

            high = middle - 1;
        }else if(key > array[middle]){
            
            low = middle + 1;
        }else{
            return middle;
        }
    }
    return 0;
}

void Binary_Sear(){
    int arr[] = {23,45,1,43,87,5,4,98,77};
    int len = 9;
    int key = 5;
    
    //先排序
    int i,j;
    for(i=0;i<len-1;i++){
        for(j=0;j<len-i-1;j++){
            if(arr[j] > arr[j+1]){
                int t;
                t = arr[j];
                arr[j] = arr[j+1];
                arr[j+1] = t;
            }
        }
    }
    
    printf("after sort arr[]:");
    for(i=0;i<len-1;i++){
        printf(" %d ",arr[i]);
    }
    
    printf("\nkey(%d) is in %d   ",key,Binary_Search(arr,len,key)); //二分查找
}
//end

/*
插值查找（折半查找的改进）
把middle = (low+high)/2;
改为middle = low + (high - low) * (key - array[low]) / (array[high] - array[low]);
把原来的1/2改进成(key - array[low]) / (array[high] - array[low])
平均效率要比折半查找好的多
*/


int Fibonacci_Search(int *array, int len, int key){
    int F[] = {0,1,1,2,3,5,8,13,21,34,55,89};

    int low,high,mid,i,k;
    low = 1;
    high = len;
    k = 0;
    while(len > F[k]-1){
        k++;
    }
    for(i=len;i<F[k]-1;i++){
        array[i] = array[len];
    }
    while(low <= high){
        mid = low+F[k-1]-1;
        if(key < array[mid]){
            high = mid -1;
            k = k - 1;
        }else if(key > array[mid]){
            low = mid + 1;
            k = k - 2;
        }else{
            if(mid <= len){
                return mid;
            }else{
                return len;
            }
        }
    }
    return 0;
}
void Fibonacci_Sear(){
    int arr[] = {0,23,45,1,43,87,5,4,98,77};
    int len = 10;
    int key = 77;
    
    //先排序
    int i,j;
    for(i=0;i<len-1;i++){
        for(j=0;j<len-i-1;j++){
            if(arr[j] > arr[j+1]){
                int t;
                t = arr[j];
                arr[j] = arr[j+1];
                arr[j+1] = t;
            }
        }
    }
    
    printf("after sort arr[]:");
    for(i=0;i<len;i++){
        printf(" %d ",arr[i]);
    }
    
    printf("\nkey(%d) is in %d   ",key,Fibonacci_Search(arr,len-1,key)); //
}

int main(){

    //Sequential_Sear();//顺序查找
//    Binary_Sear();//折半查找
    Fibonacci_Sear();



    return 0;
}