给出一颗二叉树。找到两个值的最小公共节点。

假设两个值都会在树中出现。

假设可能不会出现的话，也非常easy。就查找一遍看两个值是否在树中就能够了。假设不在就直接返回NULL。

基本思想：就是在二叉树中比較节点值和两个值的大小，假设都在一边（左边或者右边）那么就往下继续查找，否则就是都在同一边了，那么就能够返回这个节点了，这个节点就是最低公共单亲节点了。

參考：http://www.geeksforgeeks.org/lowest-common-ancestor-in-a-binary-search-tree/


#include <stdio.h>
#include <stdlib.h>

class LCABST
{
  struct Node
  {
    int data;
    Node *left, *right;
    Node(int d) : data(d), left(NULL), right(NULL) {}
  };
  Node *lca(Node *root, int n1, int n2)
  {
    if (!root) return NULL;
    if (n1 < root->data && n2 < root->data) 
      return lca(root->left, n1, n2);
    if (root->data < n1 && root->data < n2)
      return lca(root->right, n1, n2);
    return root;
  }

  Node *lcaIter(Node *root, int n1, int n2)
  {
    while (root)
    {
      if (n1 < root->data && n2 < root->data)
        root = root->left;
      else if (root->data < n1 && root->data < n2)
        root = root->right;
      else break;
    }
    return root;
  }

  Node *root;
public:
  LCABST()
  {
    run();
  }

  void run()
  {
    // Let us construct the BST shown in the above figure
    root = new Node(20);
    root->left = new Node(8);
    root->right = new Node(22);
    root->left->left = new Node(4);
    root->left->right = new Node(12);
    root->left->right->left = new Node(10);
    root->left->right->right = new Node(14);

    int n1 = 10, n2 = 14;
    Node *t = lca(root, n1, n2);
    printf("LCA of %d and %d is %d \n", n1, n2, t->data);

    n1 = 14, n2 = 8;
    t = lca(root, n1, n2);
    printf("LCA of %d and %d is %d \n", n1, n2, t->data);

    n1 = 10, n2 = 22;
    t = lca(root, n1, n2);
    printf("LCA of %d and %d is %d \n", n1, n2, t->data);

    n1 = 10, n2 = 14;
    printf("\nIterative Run:\n");
    t = lcaIter(root, n1, n2);
    printf("LCA of %d and %d is %d \n", n1, n2, t->data);

    n1 = 14, n2 = 8;
    t = lcaIter(root, n1, n2);
    printf("LCA of %d and %d is %d \n", n1, n2, t->data);

    n1 = 10, n2 = 22;
    t = lcaIter(root, n1, n2);
    printf("LCA of %d and %d is %d \n", n1, n2, t->data);
  }
  ~LCABST()
  {
    deleteTree(root);
  }
  void deleteTree(Node *r)
  {
    if (!r) return;
    deleteTree(r->left);
    deleteTree(r->right);
    delete r; r = NULL;
  }
};



Geeks LCA最低公共单亲节点_二叉树