二分查找法

public static int binarySearch(int a[], int value){

int left = 0;

int right = a.length - 1;

while (left <= right) {

int index = (left + right) / 2;

if (value < a[index]) {

right = right - 1;

} else if (value > a[index]) {

left = left + 1;

} else {

return index;

}

}

return -1;

}