二分查找

注意必须是排好序的数组

方法一：

public static int binarySearch(int[] array,int n){
int start=0;
int end=array.length-1;
int middle=(start+end)/2;
while(start<=end){
if(n>array[middle]){
start=middle+1;
}else if(n<array[middle]){
end=middle-1;
}else{
return middle;
}
}
return -1;
}

方法二：递归
/**
* 递归写法
* @param array
* @param n
* @param start
* @param end
* @return
*/
public static int binarySearch(int[] array,int n,int start,int end){
int middle=(start+end)/2;
if(n>array[end] || n<array[start] || start>end){
return -1;
}
if(n>array[middle]){
return binarySearch(array, n, middle+1, end);
}else if(n<array[middle]){
return binarySearch(array, n, start, middle-1);
}else{
return middle;
}
}