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递归:函数自己调用自己
二分(折半)查找:在一个有序的列表中,要查找某值X。
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每次取该列表最中间位置的值M与待查找值X进行比较。
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若X>M,说明待找值X可能在右半区间(大的区间——这取决于列表是从小到大还是从大到小,假设此时列表从小到大排列)内;
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若X<M,说明待找值X可能在左半区间内;
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故可将列表范围缩小为一个仅有原来一半大小的区间内重复操作。
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若最终有X=M,则说明查找成功;
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若当low>high时,仍然未找到,则说明查找失败。
C语言递归版
#include<stdio.h>
int bin_find_dg(int* test, int low, int high,int find)
{
int mid = (low + high) / 2;
if (low > high)
return -1;
else if (find == *(test + mid))
return mid;
else if (find < *(test + mid))
{
high = mid - 1;
bin_find_dg(test, low, high, find);
}
else if (find > *(test + mid))
{
low = mid + 1;
bin_find_dg(test, low, high, find);
}
}
int main()
{
int test[9] = { 1,2,3,4,5,6,7,8,9 };
int temp = bin_find_dg(test, 0, 8, -4);
if( -1==temp )
printf("Not Find!");
else
printf("Find it:%d!",temp);
return 0;
}
C语言非递归版
int bin_find_fdg(int* test, int low, int high, int find)
{
int mid;
while (low <= high)
{
mid = (low + high) / 2;
if (find == *(test + mid))
return mid;
else if (find < *(test + mid))
high = mid - 1;
else if (find > *(test + mid))
low = mid + 1;
}
return -1;
}
int main()
{
int test[9] = { 1,2,3,4,5,6,7,8,9 };
int temp = bin_find_fdg(test, 0, 8, 9);
if( -1==temp )
printf("Not Find!");
else
printf("Find it! Location:%d!",temp);
return 0;
}
Python非递归版
def binary_search(list, item):
low = 0
high = len(list) - 1
while low <= high:
mid = (low + high)
guess = list[mid]
if guess == item:
return mid
if guess > item:
high = mid - 1
else:
low = mid + 1
return None
my_list = [1, 3, 5, 7, 9]
print( binary_search(my_list, 3) ) # => 1
print( binary_search(my_list, -1) )# => None