单选题：对于下列二分查找的算法，正确的是________。

对于下列二分查找的算法，正确的是________。
@[D](2)

A. ```c++
int binarySearch(int a[], int n, int x) {
int low = 0, high = n - 1;
while (low <= high) {
int mid = (low + high) / 2;
if (x == a[mid])return mid;
else if (x > a[mid])low = mid;
else high = mid;
}
return -1;
}
```
B. ```c++
int binarySearch(int a[], int n, int x) {
int low = 0, high = n - 1;
while (low + 1 != high) {
int mid = (low + high) / 2;
if (x >= a[mid])low = mid;
else high = mid;
}
if (x == a[low])return low;
else return -1;
}
```
C. ```c++
int binarySearch(int a[], int n, int x) {
int low = 0, high = n - 1;
while (low < high - 1) {
int mid = (low + high) / 2;
if (x < a[mid])high = mid;
else low = mid;
}
if (x == a[low])return low;
else return -1;
}
```
D. ```c++
int binarySearch(int a[], int n, int x) {
if (n > 0 && x >= a[0]) {
int low = 0, high = n - 1;
while (low < high) {
int mid = (low + high + 1) / 2;
if (x < a[mid])high = mid - 1;
else low = mid;
}
if (x == a[low])return low;
}
return -1;
}
```



A.```c++
int binarySearch(int a[], int n, int x) {
int low = 0, high = n - 1;
while (low <= high) {
int mid = (low + high) / 2;
if (x == a[mid])return mid;
else if (x > a[mid])low = mid;
else high = mid;
}
return -1;
}
```
B.```c++
int binarySearch(int a[], int n, int x) {
int low = 0, high = n - 1;
while (low + 1 != high) {
int mid = (low + high) / 2;
if (x >= a[mid])low = mid;
else high = mid;
}
if (x == a[low])return low;
else return -1;
}
```
C.```c++
int binarySearch(int a[], int n, int x) {
int low = 0, high = n - 1;
while (low < high - 1) {
int mid = (low + high) / 2;
if (x < a[mid])high = mid;
else low = mid;
}
if (x == a[low])return low;
else return -1;
}
```
D.```c++
int binarySearch(int a[], int n, int x) {
if (n > 0 && x >= a[0]) {
int low = 0, high = n - 1;
while (low < high) {
int mid = (low + high + 1) / 2;
if (x < a[mid])high = mid - 1;
else low = mid;
}
if (x == a[low])return low;
}
return -1;
}
```


答案：D