C经典算法之二分查找法

#include <stdio.h>/* 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;}

#include <stdio.h>/* 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;}