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1.根据key查找所在数组的位置

#include 
   
    /* key = 9; 1   2  3   4   5    6   7    8 arr   3， 4， 5， 7， 9 ， 11， 21， 23 low = 1      mid = (low + high)/2 = 4                       high = 8; one            arr[mid] = 7 < 9;     so    low = mid + 1 = 5; high = 8;    mid = (low + high)/2 = 6 two            arr[mid] = 11 > 9     so    low = 5 ,          high = mid - 1 = 5 mid = 5; arr[mid] = 9 == key if(key = 10)   low = mid + 1 > high */int main(int argc, const char * argv[]){    int findByHalf(int arr[], int len, int key);    int arr[] = {
  3, 4 ,  5, 7, 9 , 11, 21, 23};    int len = sizeof(arr)/sizeof(int);    int index = findByHalf(arr, len, 88);    printf("index = %d\n", index);    return 0;}int findByHalf(int arr[], int len, int key){    int low = 0;    int high = len - 1;    int mid ;    while(low <= high){        mid = (low + high) / 2;        //右边查找        if (key > arr[mid]) {            low = mid + 1;        //左边查找        }else if (key > arr[mid]) {            high = mid - 1;        }else{            return mid;        }    }    return  -1;}
   

2.插入一个数，得到其所在数组的位置

#include 
   
    /* key = 9; 1   2  3   4   5    6   7    8 arr   3， 4， 5， 7， 9 ， 11， 21， 23 low = 1      mid = (low + high)/2 = 4                       high = 8; one            arr[mid] = 7 < 9;     so    low = mid + 1 = 5; high = 8;    mid = (low + high)/2 = 6 two            arr[mid] = 11 > 9     so    low = 5 ,          high = mid - 1 = 5 mid = 5; arr[mid] = 9 == key if(key = 10)   low = mid + 1 > high */int main(int argc, const char * argv[]){    int findByHalf(int arr[], int len, int key);    int arr[] = {
  3, 4 ,  5, 7, 9 , 11, 21, 23};    int len = sizeof(arr)/sizeof(int);    int index = findByHalf(arr, len, 88);    printf("index = %d\n", index);    return 0;}int insertByHalf(int arr[], int len, int key){    int low = 0;    int high = len - 1;    int mid ;    while(low <= high){        mid = (low + high) / 2;        //右边查找        if (key > arr[mid]) {            low = mid + 1;        //左边查找        }else if (key > arr[mid]) {            high = mid - 1;        }else{            //如果arr[mid] == key            //就把key插入到这个数的后面            return mid + 1;        }    }    //如果low > high 说明 key > arr[mid];    //就把key插入到low对应的 这个数的位置    return  low;}
   

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