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比较两组二叉树

compareto binary-tree recursion java

user6264051 · 技术社区 · 8 年前

我应该创建一个equals()方法来比较两棵树。 ,如果它包含第一棵树的所有元素,则应返回true。

我的方法是,使用递归,逐步遍历第二棵树,并将其与第一棵树的一个节点进行比较。如果我得到一个匹配,我将返回true并继续使用第一棵树中的另一个节点。如果我在没有匹配的情况下通过第二棵树,我会返回false。

我的代码用于比较两棵树是否相等:

     public boolean equals(BST t) {
    return equalsTree(root, t.root);
  }

  public boolean equalsTree(Node r, Node t){
    if(r == null && t == null){
      return true; 
    }else if((r != null && t == null) || (r==null && t != null)){
      return false;
    }else{
      return t.key.equals(r.key) && (equalsTree(r.left,t.left)) && (equalsTree(r.right, t.right));
    }

  }

1 回复 | 直到 8 年前

Mr. Polywhirl 8 年前

你的想法是对的。您需要比较左右分支是否匹配。如果他们不比较对方。

|  1 | {                     |  {                     | 
|  2 |     v: 0              |      v: 0              | 
|  3 |     l: {              |      l: {              | 
|  4 |         v: 1,         |          v: 2          | 
|  5 |         l: null       |          l: null       | 
|  6 |         r: null       |          r : {         | 
|  7 |     },                |              v: 3      | 
|  8 |     r: {              |              l: null   | 
|  9 |         v: 2          |              r: null   | 
| 10 |         l: {          |          }             | 
| 11 |             v: 3      |      }                 | 
| 12 |             l: null   |       r: {             | 
| 13 |             r: null   |          v: 1          | 
| 14 |         },            |          l: null       | 
| 15 |         r: null       |          r: null       | 
| 16 |     }                 |      }                 | 
| 17 | }                     |  }                     |

树比较。Java语言

public class TreeCompare {
    public static void main(String[] args) {
        Tree<Integer> treeA = new Tree<Integer>();
        Tree<Integer> treeB = new Tree<Integer>();

        Node<Integer> treeArootNode = new Node<Integer>(0);
        Node<Integer> treeBrootNode = new Node<Integer>(0);

        Node<Integer> treeAnode1 = new Node<Integer>(1);
        Node<Integer> treeAnode2 = new Node<Integer>(2);
        Node<Integer> treeAnode3 = new Node<Integer>(3);

        Node<Integer> treeBnode1 = new Node<Integer>(1);
        Node<Integer> treeBnode2 = new Node<Integer>(2);
        Node<Integer> treeBnode3 = new Node<Integer>(3);

        treeA.root = treeArootNode;
        treeB.root = treeBrootNode;

        treeA.root.left = treeAnode1;
        treeA.root.right = treeAnode2;

        treeB.root.left = treeBnode2;
        treeB.root.right = treeBnode1;

        treeAnode2.left = treeAnode3;
        treeBnode2.right = treeBnode3; // or treeBnode2.left

        System.out.println(treeA);
        System.out.println(treeB);

        System.out.println(treeA.equals(treeB));
    }
}

public class Tree<T> {
    public Node<T> root;

    @SuppressWarnings("unchecked")
    public boolean equals(Object other) {
        Tree<T> otherTree = (Tree<T>) other;

        if (other == null) return false;
        if (this.root == null && otherTree.root != null) return false;
        if (this.root != null && otherTree.root == null) return false;

        return equalsNode(this.root, otherTree.root);
    }

    public boolean equalsNode(Node<T> nodeA, Node<T> nodeB) {
        if (nodeA == null && nodeB == null) return true;
        if (nodeA == null && nodeB != null) return false;
        if (nodeA != null && nodeB == null) return false;

        if (nodeA.equals(nodeB)) {
            if (nodeA.value == null && nodeB.value != null) return false;
            if (nodeA.value != null && nodeB.value == null) return false;

            if (nodesEqualSameLeft(nodeA, nodeB) && nodesEqualSameRight(nodeA, nodeB)) {
                return equalsNode(nodeA.left, nodeB.left) && equalsNode(nodeA.right, nodeB.right);
            }

            if (nodesEqualOppositeLeft(nodeA, nodeB) && nodesEqualOppositeRight(nodeA, nodeB)) {
                return equalsNode(nodeA.left, nodeB.right) && equalsNode(nodeA.right, nodeB.left);
            }
        }

        return false;
    }

    public boolean nodesEqualSameLeft(Node<T> nodeA, Node<T> nodeB) {
        return nodesEqual(nodeA.left, nodeB.left);
    }

    public boolean nodesEqualSameRight(Node<T> nodeA, Node<T> nodeB) {
        return nodesEqual(nodeA.right, nodeB.right);
    }

    public boolean nodesEqualOppositeLeft(Node<T> nodeA, Node<T> nodeB) {
        return nodesEqual(nodeA.left, nodeB.right);
    }

    public boolean nodesEqualOppositeRight(Node<T> nodeA, Node<T> nodeB) {
        return nodesEqual(nodeA.right, nodeB.left);
    }

    public boolean nodesEqual(Node<T> nodeA, Node<T> nodeB) {
        return (nodeA == null && nodeB == null) || (nodeA != null && nodeA.equals(nodeB));
    }

    @Override
    public String toString() {
        return root.toString();
    }
}

节点。Java语言

public class Node<T> {
    public Node<T> left;
    public Node<T> right;
    public T value;

    public Node(Node<T> left, Node<T> right, T value) {
        this.left = left;
        this.right = right;
        this.value = value; 
    }

    public Node(T value) {
        this(null, null, value);
    }

    @Override
    @SuppressWarnings("unchecked")
    public boolean equals(Object other) {
        Node<T> otherNode = (Node<T>) other;

        if (other == null) return false;
        if (this.value == null && otherNode.value != null) return false;
        if (this.value != null && otherNode.value == null) return false;

        return this.value.equals(otherNode.value);
    }

    @Override
    public String toString() {
        return String.format("{ \"v\" : %s, \"l\" : %s, \"r\" : %s }", value, left, right);
    }
}

输出

{ "v" : 0, "l" : { "v" : 1, "l" : null, "r" : null }, "r" : { "v" : 2, "l" : { "v" : 3, "l" : null, "r" : null }, "r" : null } }
{ "v" : 0, "l" : { "v" : 2, "l" : null, "r" : { "v" : 3, "l" : null, "r" : null } }, "r" : { "v" : 1, "l" : null, "r" : null } }
true