递归方法打印出太多次？

Question

所以我有一个方法可以递归地对 GeometricObjects 的数组进行排序，并按照它们的面积顺序打印出来。但是，我似乎无法弄清楚这个小问题。我的方法是正确地打印出数据，但它打印出 arraylist 6 次而不是一次（它包含 6 个对象），知道我做错了什么吗？谢谢！

private static void recursionSort(ArrayList<GeometricObject> list, int low, int high){
    if (low < high){
        int minIndex = low;
        GeometricObject min = list.get(low); //set min to first object in range
        for (int i = low + 1; i <= high; i++){ //loop through all values other than first
            if (list.get(i).getArea() < min.getArea()){ //check if the value is smaller than current min
                min = list.get(i); //if it is update the min
                minIndex = i; //store min index so we can swap locations later
            }
        }

        Collections.swap(list, low, minIndex); //move the original min to new min's old index (tricky wording)
        list.set(low, min); //set the old lowest to the new lowest using store min value

        recursionSort(list, low + 1, high); //call it again

    }
    System.out.println("Recursion sort:" + list);

}

期望的输出：

Recursion sort:[GeometricObject [color=blue, filled=false, dateOfCreation=Wed Oct 14 12:02:33 EDT 2015]
 Circle [ radius=2.0  Area=12.57  Perimeter=12.57 ]
, GeometricObject [color=green, filled=false, dateOfCreation=Wed Oct 14 12:02:33 EDT 2015]
 Circle [ radius=4.0  Area=50.27  Perimeter=25.13 ]
, GeometricObject [color=green, filled=false, dateOfCreation=Wed Oct 14 12:02:33 EDT 2015]
 Rectangle [ Height=5.0 Width= 11.0  Area=55.0  Perimeter=32.0 ]
, GeometricObject [color=orange, filled=true, dateOfCreation=Wed Oct 14 12:02:33 EDT 2015]
 Rectangle [ Height=10.0 Width= 6.0  Area=60.0  Perimeter=32.0 ]
, GeometricObject [color=red, filled=true, dateOfCreation=Wed Oct 14 12:02:33 EDT 2015]
 Rectangle [ Height=14.0 Width= 12.0  Area=168.0  Perimeter=52.0 ]
, GeometricObject [color=blue, filled=true, dateOfCreation=Wed Oct 14 12:02:33 EDT 2015]
 Circle [ radius=15.0  Area=706.86  Perimeter=94.25 ]
]

我收到的输出

Recursion sort:[GeometricObject [color=blue, filled=false, dateOfCreation=Wed Oct 14 12:02:33 EDT 2015]
 Circle [ radius=2.0  Area=12.57  Perimeter=12.57 ]
, GeometricObject [color=green, filled=false, dateOfCreation=Wed Oct 14 12:02:33 EDT 2015]
 Circle [ radius=4.0  Area=50.27  Perimeter=25.13 ]
, GeometricObject [color=green, filled=false, dateOfCreation=Wed Oct 14 12:02:33 EDT 2015]
 Rectangle [ Height=5.0 Width= 11.0  Area=55.0  Perimeter=32.0 ]
, GeometricObject [color=orange, filled=true, dateOfCreation=Wed Oct 14 12:02:33 EDT 2015]
 Rectangle [ Height=10.0 Width= 6.0  Area=60.0  Perimeter=32.0 ]
, GeometricObject [color=red, filled=true, dateOfCreation=Wed Oct 14 12:02:33 EDT 2015]
 Rectangle [ Height=14.0 Width= 12.0  Area=168.0  Perimeter=52.0 ]
, GeometricObject [color=blue, filled=true, dateOfCreation=Wed Oct 14 12:02:33 EDT 2015]
 Circle [ radius=15.0  Area=706.86  Perimeter=94.25 ]
]
Recursion sort:[GeometricObject [color=blue, filled=false, dateOfCreation=Wed Oct 14 12:02:33 EDT 2015]
 Circle [ radius=2.0  Area=12.57  Perimeter=12.57 ]
, GeometricObject [color=green, filled=false, dateOfCreation=Wed Oct 14 12:02:33 EDT 2015]
 Circle [ radius=4.0  Area=50.27  Perimeter=25.13 ]
, GeometricObject [color=green, filled=false, dateOfCreation=Wed Oct 14 12:02:33 EDT 2015]
 Rectangle [ Height=5.0 Width= 11.0  Area=55.0  Perimeter=32.0 ]
, GeometricObject [color=orange, filled=true, dateOfCreation=Wed Oct 14 12:02:33 EDT 2015]
 Rectangle [ Height=10.0 Width= 6.0  Area=60.0  Perimeter=32.0 ]
, GeometricObject [color=red, filled=true, dateOfCreation=Wed Oct 14 12:02:33 EDT 2015]
 Rectangle [ Height=14.0 Width= 12.0  Area=168.0  Perimeter=52.0 ]
, GeometricObject [color=blue, filled=true, dateOfCreation=Wed Oct 14 12:02:33 EDT 2015]
 Circle [ radius=15.0  Area=706.86  Perimeter=94.25 ]
]
Recursion sort:[GeometricObject [color=blue, filled=false, dateOfCreation=Wed Oct 14 12:02:33 EDT 2015]
 Circle [ radius=2.0  Area=12.57  Perimeter=12.57 ]
, GeometricObject [color=green, filled=false, dateOfCreation=Wed Oct 14 12:02:33 EDT 2015]
 Circle [ radius=4.0  Area=50.27  Perimeter=25.13 ]
, GeometricObject [color=green, filled=false, dateOfCreation=Wed Oct 14 12:02:33 EDT 2015]
 Rectangle [ Height=5.0 Width= 11.0  Area=55.0  Perimeter=32.0 ]
, GeometricObject [color=orange, filled=true, dateOfCreation=Wed Oct 14 12:02:33 EDT 2015]
 Rectangle [ Height=10.0 Width= 6.0  Area=60.0  Perimeter=32.0 ]
, GeometricObject [color=red, filled=true, dateOfCreation=Wed Oct 14 12:02:33 EDT 2015]
 Rectangle [ Height=14.0 Width= 12.0  Area=168.0  Perimeter=52.0 ]
, GeometricObject [color=blue, filled=true, dateOfCreation=Wed Oct 14 12:02:33 EDT 2015]
 Circle [ radius=15.0  Area=706.86  Perimeter=94.25 ]
]
Recursion sort:[GeometricObject [color=blue, filled=false, dateOfCreation=Wed Oct 14 12:02:33 EDT 2015]
 Circle [ radius=2.0  Area=12.57  Perimeter=12.57 ]
, GeometricObject [color=green, filled=false, dateOfCreation=Wed Oct 14 12:02:33 EDT 2015]
 Circle [ radius=4.0  Area=50.27  Perimeter=25.13 ]
, GeometricObject [color=green, filled=false, dateOfCreation=Wed Oct 14 12:02:33 EDT 2015]
 Rectangle [ Height=5.0 Width= 11.0  Area=55.0  Perimeter=32.0 ]
, GeometricObject [color=orange, filled=true, dateOfCreation=Wed Oct 14 12:02:33 EDT 2015]
 Rectangle [ Height=10.0 Width= 6.0  Area=60.0  Perimeter=32.0 ]
, GeometricObject [color=red, filled=true, dateOfCreation=Wed Oct 14 12:02:33 EDT 2015]
 Rectangle [ Height=14.0 Width= 12.0  Area=168.0  Perimeter=52.0 ]
, GeometricObject [color=blue, filled=true, dateOfCreation=Wed Oct 14 12:02:33 EDT 2015]
 Circle [ radius=15.0  Area=706.86  Perimeter=94.25 ]
]
Recursion sort:[GeometricObject [color=blue, filled=false, dateOfCreation=Wed Oct 14 12:02:33 EDT 2015]
 Circle [ radius=2.0  Area=12.57  Perimeter=12.57 ]
, GeometricObject [color=green, filled=false, dateOfCreation=Wed Oct 14 12:02:33 EDT 2015]
 Circle [ radius=4.0  Area=50.27  Perimeter=25.13 ]
, GeometricObject [color=green, filled=false, dateOfCreation=Wed Oct 14 12:02:33 EDT 2015]
 Rectangle [ Height=5.0 Width= 11.0  Area=55.0  Perimeter=32.0 ]
, GeometricObject [color=orange, filled=true, dateOfCreation=Wed Oct 14 12:02:33 EDT 2015]
 Rectangle [ Height=10.0 Width= 6.0  Area=60.0  Perimeter=32.0 ]
, GeometricObject [color=red, filled=true, dateOfCreation=Wed Oct 14 12:02:33 EDT 2015]
 Rectangle [ Height=14.0 Width= 12.0  Area=168.0  Perimeter=52.0 ]
, GeometricObject [color=blue, filled=true, dateOfCreation=Wed Oct 14 12:02:33 EDT 2015]
 Circle [ radius=15.0  Area=706.86  Perimeter=94.25 ]
]
Recursion sort:[GeometricObject [color=blue, filled=false, dateOfCreation=Wed Oct 14 12:02:33 EDT 2015]
 Circle [ radius=2.0  Area=12.57  Perimeter=12.57 ]
, GeometricObject [color=green, filled=false, dateOfCreation=Wed Oct 14 12:02:33 EDT 2015]
 Circle [ radius=4.0  Area=50.27  Perimeter=25.13 ]
, GeometricObject [color=green, filled=false, dateOfCreation=Wed Oct 14 12:02:33 EDT 2015]
 Rectangle [ Height=5.0 Width= 11.0  Area=55.0  Perimeter=32.0 ]
, GeometricObject [color=orange, filled=true, dateOfCreation=Wed Oct 14 12:02:33 EDT 2015]
 Rectangle [ Height=10.0 Width= 6.0  Area=60.0  Perimeter=32.0 ]
, GeometricObject [color=red, filled=true, dateOfCreation=Wed Oct 14 12:02:33 EDT 2015]
 Rectangle [ Height=14.0 Width= 12.0  Area=168.0  Perimeter=52.0 ]
, GeometricObject [color=blue, filled=true, dateOfCreation=Wed Oct 14 12:02:33 EDT 2015]
 Circle [ radius=15.0  Area=706.86  Perimeter=94.25 ]
]

Answer 1

您正在递归方法的末尾打印列表。因为每次调用都会发生这种情况，所以一旦最内层的递归调用完成，每次递归调用都会打印列表。

将递归方法之外的打印移动到刚好进行初始递归调用之后。

Answer 2

这里的问题是每一层递归都会在返回前打印出列表。

要修复，您可以重载打印方法：

private static void recursionSort(ArrayList<GeometricObject> list){
    recursionSort(list, 0, list.size())
    System.out.println("Recursion sort:" + list);        
}

private static void recursionSort(ArrayList<GeometricObject> list, int low, int high){
    if (low < high){
        int minIndex = low;
        GeometricObject min = list.get(low); //set min to first object in range
        for (int i = low + 1; i <= high; i++){ //loop through all values other than first
            if (list.get(i).getArea() < min.getArea()){ //check if the value is smaller than current min
                min = list.get(i); //if it is update the min
                minIndex = i; //store min index so we can swap locations later
            }
        }

        Collections.swap(list, low, minIndex); //move the original min to new min's old index (tricky wording)
        list.set(low, min); //set the old lowest to the new lowest using store min value

        recursionSort(list, low + 1, high); //call it again

    }

}

Answer 3

你试过从你的函数中返回列表吗？

public static void main (String args []){
    ArrayList<GeometricObject> list = new ArrayList<GeometricObject>();
    System.out.println(recursionSort(list, 0,list.size()-1).toString());
}

private static ArrayList<GeometricObject> recursionSort(ArrayList<GeometricObject> list, int low, int high){
    if (low < high){
        int minIndex = low;
        GeometricObject min = list.get(low); 
        for (int i = low + 1; i <= high; i++){ 
            if (list.get(i).getArea() < min.getArea()){ 
                min = list.get(i); 
                minIndex = i; 
            }
        }

        Collections.swap(list, low, minIndex);
        list.set(low, min);

        recursionSort(list, low + 1, high);

    }
    return list;

}

}

输出： [0, 1, 1, 9, 10, 12, 100]

递归方法打印出太多次？

Recursion method printing out too many times?

java

recursion

arraylist

output