如何从含父子层级关系的数组中筛选顶层层级元素？

我需要一种方法，从包含父子层级关系对象的数组里筛选出顶层层级元素。以下是几个具体示例：

第一个示例数组：

[
    {
        "Code": "1A",
        "name": "Western Europe",
        "hierarchy": "World/"
    },
    {
        "Code": "AT",
        "name": "Austria",
        "hierarchy": "World/ Western Europe/"
    },
    {
        "Code": "NL",
        "name": "Netherlands",
        "hierarchy": "World/ Western Europe/"
    }
]

输出应为第一个对象，因为Western Europe是Austria和Netherlands的父级。

第二个示例数组：

[
    {
        "Code": "WO",
        "name": "World",
        "hierarchy": ""
    },
    {
        "Code": "NA",
        "name": "North America",
        "hierarchy": "World/"
    },
    {
        "Code": "NL",
        "name": "Netherlands",
        "hierarchy": "World/ Western Europe/"
    }
]

输出为World，因为它是顶层层级。

第三个示例数组：

[
    {
        "Code": "1A",
        "name": "Western Europe",
        "hierarchy": "World/"
    },
    {
        "Code": "NA",
        "name": "North America",
        "hierarchy": "World/"
    },
    {
        "Code": "US",
        "name": "United States",
        "hierarchy": "World/ North America/"
    },
    {
        "Code": "NL",
        "name": "Netherlands",
        "hierarchy": "World/ Western Europe/"
    },
    {
        "Code": "RS",
        "name": "Russia",
        "hierarchy": "World/ Eastern Europe/"
    }
]

输出应为Western Europe、North America和Russia（由于列表中没有Eastern Europe，因此Russia属于其层级的顶层）。

另外，我有一个可传入Code获取层级结构的函数：

getParentChildHierarchy(string Code) { //some code here }

函数调用示例：

• 输入: AT
• 输出: WO>1A>AT

求最优解决方案。

内容的提问来源于stack exchange，提问作者Purushottam Gupta