二分查找

public static int ef(int a[], int tag) {

int first = 0;

int end = a.length;

for (int i = 0; i < a.length; i++) {

int middle = (first + end) / 2;

if (tag == a[middle]) {

return middle;

}

if (tag > a[middle]) {

first = middle + 1;

}

if (tag < a[middle]) {

end = middle - 1;

}

}

return 0;

}