二分查找思路很简单，但要把程序写对，却很难，有兴趣的话，可以在网上查一下相关资料，下面给出两种常见的错误：(至于具体错误原因，可以分析程序的执行)
错误程序1：
1 #include <iostream> 2 using namespace std; 3 4 int binarySearch(int a[], int n, int key) 5 { 6 int low = 0; 7 int high = n - 1; 8 int mid; 9 while(low < high) //key可能刚好在low与high相等的地方 10 { 11 mid = (low + high)/2; 12 if(key == a[mid]) 13 return mid; 14 15 if(key < a[mid]) 16 high = mid - 1; 17 else 18 low = mid + 1; 19 } 20 21 return -1; 22 } 23 24 int main() 25 { 26 int a[] = {0, 1, 2}; 27 int n = 3; 28 int key = 0; 29 int result = binarySearch(a, n, key); 30 31 if(-1 == result) 32 cout << "no" << endl; 33 else 34 cout << "yes! location: " << result + 1 << endl; 35 36 return 0; 37 }
错误程序2：
1 #include <iostream> 2 using namespace std; 3 4 int binarySearch(int a[], int n, int key) 5 { 6 int low = 0; 7 int high = n - 1; 8 int mid; 9 while(low < high) //可能是死循环 10 { 11 mid = (low + high)/2; 12 if(key == a[mid]) 13 return mid; 14 15 if(key < a[mid]) 16 high = mid; 17 else 18 low = mid; 19 } 20 21 return -1; 22 } 23 24 int main() 25 { 26 int a[] = {0, 1, 2}; 27 int n = 3; 28 int key = 100; 29 int result = binarySearch(a, n, key); 30 31 if(-1 == result) 32 cout << "no" << endl; 33 else 34 cout << "yes! location: " << result + 1 << endl; 35 36 return 0; 37 }
正确程序如下：
#include <iostream> using namespace std; int binarySearch(int a[], int n, int key) { int low = 0; int high = n - 1; int mid; while(low <= high) { mid = (low + high)/2; if(key == a[mid]) return mid; if(key < a[mid]) high = mid - 1; else low = mid + 1; } return -1; } int main() { int a[] = {0, 1, 2}; int n = 3; int key = 0; int result = binarySearch(a, n, key); if(-1 == result) cout << "no" << endl; else cout << "yes! location: " << result + 1 << endl; return 0; }