剑指offer 39 - 二叉树的深度

1.先遍历二叉树的左子树的深度，然后再遍历二叉树右子树的深度。最后判断左子树和右子树的深度，如果左子树比右子树深则返回左子树深度+1,否则返回右子树深度+1。

2.判断该树是不是平衡树，我们用后序遍历的方式遍历整棵二叉树。在遍历某结点的左右子结点之后，我们可以根据它的左右子结点的深度判断它是不是平衡的，并得到当前结点的深度。当最后遍历到树的根结点的时候，也就判断了整棵二叉树是不是平衡二叉树了。

#include <iostream>#include<vector>using namespace std;structBinaryTreeNode{intm_nValue;BinaryTreeNode*m_pLeft;BinaryTreeNode*m_pRight;};BinaryTreeNode* CreateBinaryTreeNode(intvalue){  BinaryTreeNode*head = new  BinaryTreeNode[sizeof(BinaryTreeNode )];  head->m_nValue = value;  head->m_pLeft = head->m_pRight=NULL;  return head;}void ConnectTreeNodes(BinaryTreeNode*    root ,BinaryTreeNode*   left, BinaryTreeNode*   right)    {     if(root != NULL)   {   root->m_pLeft = left;   root->m_pRight = right;   }}   void DestroyTree(BinaryTreeNode*    root){if(root !=NULL){  BinaryTreeNode* left = root->m_pLeft;  BinaryTreeNode* right= root->m_pRight;    delete root;  root=NULL;  DestroyTree(left);  DestroyTree( right);}}bool  isBalanced(BinaryTreeNode* pRoot,int *depth)     //节点深度作为参数，一边遍历一边判断是否平衡{if(pRoot==NULL){*depth=0; return  true;}int left,right;if( isBalanced(pRoot->m_pLeft,&left)   &&isBalanced(pRoot->m_pRight,&right) ){ int diff = left - right;        if(diff <= 1 && diff >= -1)  //此处不能写（-1<=diff<=1），错误{*depth = left>right ? (left+1) :(right+1);      return true;}}return false;} int  TreeDepth(BinaryTreeNode* pRoot)    //节点深度  后序遍历{      if(pRoot==NULL)          return 0;                       int nLeft= TreeDepth(pRoot->m_pLeft);         int     nRight= TreeDepth(pRoot->m_pRight);        return  nLeft>nRight ? (nLeft+1) :(nRight+1);      }   bool IsBalanced(BinaryTreeNode* pRoot)    //方法2. 需要重复遍历节点多次{      if(pRoot== NULL)          return true;        int nLeftDepth = TreeDepth(pRoot->m_pLeft);      int nRightDepth = TreeDepth(pRoot->m_pRight);      int diff = nRightDepth-nLeftDepth;        if (diff>1 || diff<-1)          return false;        return IsBalanced(pRoot->m_pLeft)&&IsBalanced(pRoot->m_pRight);  }  // ====================测试代码====================void Test(char* testName, BinaryTreeNode* pRoot,bool result){    if(testName != NULL)        printf("%s begins:", testName);int depth = 0;    if(result ==  isBalanced(pRoot,&depth))printf("%s\n","passed");elseprintf("%s\n","failed");    printf("\n");}//            1//         /      \//        2        3//       / \         \   //      4  5         6  //   \        //7   void Test1(){    BinaryTreeNode* pNode1 = CreateBinaryTreeNode(1);    BinaryTreeNode* pNode2 = CreateBinaryTreeNode(2);    BinaryTreeNode* pNode3 = CreateBinaryTreeNode(3);    BinaryTreeNode* pNode4 = CreateBinaryTreeNode(4);    BinaryTreeNode* pNode5 = CreateBinaryTreeNode(5);BinaryTreeNode* pNode6 = CreateBinaryTreeNode(6);    BinaryTreeNode* pNode7 = CreateBinaryTreeNode(7);    ConnectTreeNodes(pNode1, pNode2, pNode3);    ConnectTreeNodes(pNode2, pNode4, pNode5);ConnectTreeNodes(pNode3, NULL, pNode6);    ConnectTreeNodes(pNode5, NULL, pNode7);       Test("Test1", pNode1,true);    DestroyTree(pNode1);}//               1//              ///             2//            ///           3//          ///         4//        ///       5void Test2(){    BinaryTreeNode* pNode1 = CreateBinaryTreeNode(1);    BinaryTreeNode* pNode2 = CreateBinaryTreeNode(2);    BinaryTreeNode* pNode3 = CreateBinaryTreeNode(3);    BinaryTreeNode* pNode4 = CreateBinaryTreeNode(4);    BinaryTreeNode* pNode5 = CreateBinaryTreeNode(5);    ConnectTreeNodes(pNode1, pNode2, NULL);    ConnectTreeNodes(pNode2, pNode3, NULL);    ConnectTreeNodes(pNode3, pNode4, NULL);    ConnectTreeNodes(pNode4, pNode5, NULL);    Test("Test2",pNode1, false);    DestroyTree(pNode1);}// 1//  \//   2//    \//     3//      \//       4//        \//         5void Test3(){    BinaryTreeNode* pNode1 = CreateBinaryTreeNode(1);    BinaryTreeNode* pNode2 = CreateBinaryTreeNode(2);    BinaryTreeNode* pNode3 = CreateBinaryTreeNode(3);    BinaryTreeNode* pNode4 = CreateBinaryTreeNode(4);    BinaryTreeNode* pNode5 = CreateBinaryTreeNode(5);    ConnectTreeNodes(pNode1, NULL, pNode2);    ConnectTreeNodes(pNode2, NULL, pNode3);    ConnectTreeNodes(pNode3, NULL, pNode4);    ConnectTreeNodes(pNode4, NULL, pNode5);    Test("Test3",pNode1, false);    DestroyTree(pNode1);}// 树中只有1个结点void Test4(){    BinaryTreeNode* pNode1 = CreateBinaryTreeNode(1);    Test("test4",pNode1, true);    DestroyTree(pNode1);}// 树中没有结点void Test5(){Test("Test5",NULL,true);}int main(int argc, char* argv[]){    Test1();Test2();    Test3();    Test4();    Test5();        return 0;}