解决java算法的bug

Question

‘下面的代码可以很好地处理某些输入，而不能处理其他输入。该代码是给定n=列表长度的循环链表的实现，以及要采取的删除节点的k=步骤。其意图是删除增量为k的节点，例如如果1,2，3和k =2，那么要删除的第一个节点是2，然后是1，因此最后一个节点将是3代码上有2个测试用例，第一个是n=12 k=4，结果应该是1，但我在最后一个消除步骤得到了2，由于某种原因，它弄乱了秒测试用例是n=12 k=3，结果应该是10，这是正常的，所以我不知道是否有人能识别购买，谢谢。

 public static int whoIsElected(int n, int k) {
    LinkedList<Integer> circle = new LinkedList<>();
    for(int i=1;i<=n;i++)
    {
        circle.add(i);
    }
    int posToDel = k;

    if(n==1)
    {
        return 1;
    }
    if(posToDel>n)
    {
        posToDel=posToDel%n;
    }
    while(circle.size()>1)
    {
        if(posToDel==0)// becasue the posToDel-1 when posToDel ==0 is the last index
        {
            circle.remove(n-1);
        }
        else
        {
            circle.remove(posToDel-1);
        }
        n--; // decrease the length of n by 1 when u delete one from the list
        // after removing the posToDel in circle

        // this if else set the new posToDel
        if(posToDel==0)
        {
            posToDel=n-1;
        }
        else
        {
            posToDel=posToDel-1;
        }
        if(posToDel+k>n)
        {
            posToDel=(posToDel+k)%n;
        }
        else
        {
            posToDel=posToDel+k;
        }
    }
    return circle.get(0);
}

/**
 * bool doTestsPass()
 * Runs various tests. Returns true if tests pass. Otherwise,
 * returns false.
 */
public static boolean doTestsPass() {
    // todo: implement more tests, please
    // feel free to make testing more elegant
    // test cases are structered as {n, k, expected answer}
    int[][] testCases = {
            {12, 4, 1},// give wrong answer
            {12, 3, 10}// give right answer
    };

    for (int[] testCase : testCases) {
        int answer = whoIsElected(testCase[0], testCase[1]);
        if (answer != testCase[2]) {
            System.out.println("test failed!");
            System.out.printf("n:%d, k%d, answer got: %d, should be: %d\n", testCase[0], testCase[1], answer, testCase[2]);
            return false;
        }
    }
    System.out.println("All tested passed");
    return true;
}

/**
 * Execution entry point.
 */
public static void main(String args[]) {
    doTestsPass();
}

}

Answer 1

我猜当只剩下3个元素时，问题就出现了[1,2,9]

因此，当手动尝试时，当要删除元素9时，posToDel应该为3，但当我们在代码中运行时，posToDel值为0。

您可以尝试在不同的时间点添加控制台日志和跟踪值。但它可能会很快变得混乱，你可能最终会花费比所需更多的时间。

然而，我可以建议你在循环逻辑中尝试以下算法：

在循环之前赋值posToDel= k-1，这样你就不必每次都在循环中执行posToDel-1 (只会让在循环中构建不同的逻辑变得更容易，特殊情况更少)

我已经尝试了下面的循环逻辑，它很适合你的测试用例：

while( circle.size() > 1 )
        {
            int temp = circle.remove( posToDel );
            System.out.println( temp );
            n--;
            posToDel = posToDel - 1;
            System.out.println( "after deletion of " + temp + ", pos is: " + posToDel );
            if( posToDel + k >= n )
            {
                posToDel = ( posToDel + k ) % n;
            }
            else
            {
                posToDel = posToDel + k;
            }
        }

我添加了2条sysout语句，以了解删除的顺序，这可能有助于调试

Answer 2

感谢大家关注这篇文章，我想这是正确的代码

public class WhoIsElected {

public static int whoIsElected(int n, int k) {

    /*******************************************start solution*******************************/
    LinkedList<Integer> circle = new LinkedList<>();
    for(int i=1;i<=n;i++)
    {
        circle.add(i);
    }
    int posToDel = k;

    if(n==1)
    {
        return 1;
    }
    if(posToDel>n)
    {
        posToDel=posToDel%n;
    }
    while(circle.size()>1)
    {
        if(posToDel==0)// becasue the posToDel-1 when posToDel ==0 is the last index
        {
            circle.remove(n-1);
        }
        else
        {
            circle.remove(posToDel-1);
        }
        n--; // decrease the length of n by 1 when u delete one from the list
        // after removing the posToDel in circle

        if(posToDel>0)
        {
            posToDel=posToDel-1;
        }
        if(posToDel+k>n)
        {
            posToDel=(posToDel+k)%n;
        }
        else
        {
            posToDel=posToDel+k;
        }
    }
    return circle.get(0);
    /*******************************************end solution*******************************/
}


/**
 * bool doTestsPass()
 * Runs various tests. Returns true if tests pass. Otherwise,
 * returns false.
 */
public static boolean doTestsPass() {
    // todo: implement more tests, please
    // feel free to make testing more elegant
    // test cases are structered as {n, k, expected answer}
    int[][] testCases = {
            {1, 1, 1},
            {2, 2, 1},
            {2, 5, 2},// my add test to have k bigger than n
            {100, 2, 73},
            {4,2,1},
            {5, 3, 4},
            {6, 4, 5},
            {12, 4, 1},
            {12, 3, 10},
            {1000,5,763}
    };

    for (int[] testCase : testCases) {
        int answer = whoIsElected(testCase[0], testCase[1]);
        if (answer != testCase[2]) {
            System.out.println("test failed!");
            System.out.printf("n:%d, k%d, answer got: %d, should be: %d\n", testCase[0], testCase[1], answer, testCase[2]);
            return false;
        }
    }
    System.out.println("All tested passed");
    return true;
}

/**
 * Execution entry point.
 */
public static void main(String args[]) {
    doTestsPass();
}
class Node {

}

}