JavaScript中嵌套对象结构中的递归树搜索

Question

我试图弄清楚如何递归地在这个 JSON 对象中搜索一个节点。我尝试了一些东西但无法得到它：

var tree = {
    "id": 1,
    "label": "A",
    "child": [
        {
            "id": 2,
            "label": "B",
            "child": [
                {
                    "id": 5,
                    "label": "E",
                    "child": []
                },
                {
                    "id": 6,
                    "label": "F",
                    "child": []
                },
                {
                    "id": 7,
                    "label": "G",
                    "child": []
                }
            ]
        },
        {
            "id": 3,
            "label": "C",
            "child": []
        },
        {
            "id": 4,
            "label": "D",
            "child": [
                {
                    "id": 8,
                    "label": "H",
                    "child": []
                },
                {
                    "id": 9,
                    "label": "I",
                    "child": []
                }
            ]
        }
    ]
};

这是我的非工作解决方案，这可能是因为第一个节点只是一个值，而孩子们在数组中：

function scan(id, tree) {
    if(tree.id == id) {
        return tree.label;
    }

    if(tree.child == 0) {
        return
    }

    return scan(tree.child);
};

Answer 1

您的代码只是缺少一个循环来检查child 数组中节点的每个子节点。此递归函数将返回节点的label 属性，如果树中不存在标签，则返回undefined：

const search = (tree, target) => {
  if (tree.id === target) {
    return tree.label;
  }
  
  for (const child of tree.child) {
    const found = search(child, target);
    
    if (found) {
      return found;
    }
  }
};

const tree = {"id":1,"label":"A","child":[{"id":2,"label":"B","child":[{"id":5,"label":"E","child":[]},{"id":6,"label":"F","child":[]},{"id":7,"label":"G","child":[]}]},{"id":3,"label":"C","child":[]},{"id":4,"label":"D","child":[{"id":8,"label":"H","child":[]},{"id":9,"label":"I","child":[]}]}]};

console.log(search(tree, 1));
console.log(search(tree, 6));
console.log(search(tree, 99));

您也可以使用不会导致堆栈溢出的显式堆栈进行迭代（但请注意，由于扩展语法，速记 stack.push(...curr.child); 可能会溢出某些 JS 引擎的参数大小，因此请使用显式循环或 concat 用于大型子数组）：

const search = (tree, target) => {
  for (const stack = [tree]; stack.length;) {
    const curr = stack.pop();
    
    if (curr.id === target) {
      return curr.label;
    }

    stack.push(...curr.child);
  }
};

const tree = {"id":1,"label":"A","child":[{"id":2,"label":"B","child":[{"id":5,"label":"E","child":[]},{"id":6,"label":"F","child":[]},{"id":7,"label":"G","child":[]}]},{"id":3,"label":"C","child":[]},{"id":4,"label":"D","child":[{"id":8,"label":"H","child":[]},{"id":9,"label":"I","child":[]}]}]};

for (let i = 0; ++i < 12; console.log(search(tree, i)));

更通用的设计会返回节点本身，并让调用者访问.label 属性，如果他们愿意，或者以其他方式使用对象。

请注意，JSON 纯粹是一种用于序列化（字符串化、原始）数据的字符串格式。一旦您将 JSON 反序列化为 JavaScript 对象结构（如此处所示），它就不再是 JSON。

Answer 2

scan 可以使用第三个参数递归编写，该参数模拟要扫描的节点队列

const scan = (id, tree = {}, queue = [ tree ]) =>
  // if id matches node id, return node label
  id === tree.id
    ? tree.label

  // base case: queue is empty
  // id was not found, return false
  : queue.length === 0
    ? false

  // inductive case: at least one node
  // recur on next tree node, append node children to queue
  : scan (id, queue[0], queue.slice(1).concat(queue[0].child))

因为 JavaScript 支持默认参数，所以 scan 的调用站点不会改变

console.log
  ( scan (1, tree)  // "A"
  , scan (3, tree)  // "C"
  , scan (9, tree)  // "I"
  , scan (99, tree) // false
  )

在下面的浏览器中验证它是否有效

const scan = (id, tree = {}, queue = [ tree ]) =>
  id === tree.id
    ? tree.label
  : queue.length === 0
    ? false
  : scan (id, queue[0], queue.slice(1).concat(queue[0].child))

const tree =
  { id: 1
  , label: "A"
  , child:
      [ { id: 2
        , label: "B"
        , child:
            [ { id: 5
              , label: "E"
              , child: []
              }
            , { id: 6
              , label: "F"
              , child: []
              }
            , { id: 7
              , label: "G"
              , child: []
              }
            ]
        }
      , { id: 3
        , label: "C"
        , child: []
        }
      , { id: 4
        , label: "D"
        , child:
            [ { id: 8
              , label: "H"
              , child: []
              }
            , { id: 9
              , label: "I"
              , child: []
              }
            ]
        }
      ]
  }

console.log
  ( scan (1, tree)  // "A"
  , scan (3, tree)  // "C"
  , scan (9, tree)  // "I"
  , scan (99, tree) // false
  )

相关recursive search using higher-order functions

Answer 3

这是使用object-scan的解决方案

// const objectScan = require('object-scan');

const tree = {"id":1,"label":"A","child":[{"id":2,"label":"B","child":[{"id":5,"label":"E","child":[]},{"id":6,"label":"F","child":[]},{"id":7,"label":"G","child":[]}]},{"id":3,"label":"C","child":[]},{"id":4,"label":"D","child":[{"id":8,"label":"H","child":[]},{"id":9,"label":"I","child":[]}]}]};

const search = (obj, id) => objectScan(['**.id'], {
  abort: true,
  filterFn: ({ value, parent, context }) => {
    if (value === id) {
      context.push(parent.label);
      return true;
    }
    return false;
  }
})(obj, [])[0];

console.log(search(tree, 1));
// => A
console.log(search(tree, 6));
// => F
console.log(search(tree, 99));
// => undefined

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<script src="https://bundle.run/object-scan@13.7.1"></script>

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