二分法查找

两种： 循环或递归

• 循环 详细戳这里

    public static int binarySearch(int searchKey,int[] array){
        int low=0;
        int high=array.length-1;
        while (low<=high){
            int middle=(low+high)>>1;
            if (searchKey==array[middle]){
                return middle;
            }else if (searchKey<array[middle]){
                high=middle-1;
            }else {
                low=middle+1;
            }
        }
        return ~low;
    }

• 递归
  调用：binarySearchRecursion(key,a,0,a.length)

public static int binarySearchRecursion(int searchKey,int[] array,int lowIndex,int highIndex){
        if (searchKey<array[lowIndex] || searchKey>array[highIndex] || lowIndex>highIndex){
            return ~lowIndex;
        }
        int middleIndex=(lowIndex+highIndex)>>1;
        if (searchKey<array[middleIndex]){
            return binarySearchRecursion(searchKey,array,lowIndex,middleIndex-1);
        }else if (searchKey>array[middleIndex]){
            return binarySearchRecursion(searchKey,array,middleIndex+1,highIndex);
        }else {
            return middleIndex;
        }
    }