/**
 * 循環實現二分查找算法
 */
public static int binarySearch(int[] arr, int x){
    int low = 0;
    int high = arr.length - 1;
    while(low <= high){
        int middle = (low + high)/2;
        if (x == arr[middle]){
            return middle;
        }else if(x < arr[middle]){
            high = middle - 1;
        }else{
            low = middle + 1;
        }
    }
    return -1;
}

/**
 * 遞歸查找
 */
public static int binarySearchRecursive(int[] arr, int x, int startIndex, int endIndex){
    int middle = (startIndex + endIndex) / 2;
    //三個終止條件
    if(x < arr[startIndex] || x > arr[endIndex] || startIndex > endIndex){
        return -1;
    }
    if (x < arr[middle]){
        return binarySearchRecursive(arr, x, startIndex, middle - 1);
    }else if (x > arr[middle]){
        return binarySearchRecursive(arr, x, middle + 1, endIndex);
    }else{
        return middle;
    }
}

【數據結構】二分查找