c语言二分法插入排序算法,C经典算法之二分查找法

C经典算法之二分查找法

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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