（算法）二叉树两个结点的最远距离

class TreeNode{
public:
    int val;
    TreeNode* left;
    TreeNode* right;
    TreeNode(int x):val(x),left(NULL),right(NULL){}
};

class Node{
public:
    int val;
    Node* left;
    Node* right;
    int maxLeft;
    int maxRight;
};

void longestPath_1(Node* pRoot,int& maxLen){
    if(pRoot==NULL)
        return;
    if(pRoot->left==NULL)
        pRoot->maxLeft=0;
    if(pRoot->right==NULL)
        pRoot->maxRight=0;

    int leftLen;
    if(pRoot->left){
        longestPath_1(pRoot->left,maxLen);
        leftLen=1+max(pRoot->left->maxLeft,pRoot->left->maxRight);
        pRoot->maxLeft=leftLen;
    }

    int rightLen;
    if(pRoot->right){
        longestPath_1(pRoot->right,maxLen);
        rightLen=1+max(pRoot->right->maxLeft,pRoot->right->maxRight);
        pRoot->maxRight=rightLen;
    }

    maxLen=max(pRoot->maxLeft+pRoot->maxRight,maxLen);
}

class TreeNode{
public:
    int val;
    TreeNode* left;
    TreeNode* right;
    TreeNode(int x):val(x),left(NULL),right(NULL){}
};

void longestPath(TreeNode* pRoot,int& maxLeft,int& maxRight,int& maxLen){
    if(pRoot==NULL){
        maxLeft=0;
        maxRight=0;
        maxLen=0;
        return;
    }

    int maxLeft_1,maxLeft_2,maxRight_1,maxRight_2;
    longestPath(pRoot->left,maxLeft_1,maxRight_1,maxLen);
    longestPath(pRoot->right,maxLeft_2,maxRight_2,maxLen);

    maxLeft=1+max(maxLeft_1,maxRight_1);
    maxRight=1+max(maxLeft_2,maxRight_2);

    maxLen=max(maxLeft,maxRight)+1;
}