11.5(树Ⅱ)

6.6最小深度二叉树

class Solution {//后序遍历
public:
    int getMin(TreeNode* bt){
        if(!bt) return 0;
        int m = getMin(bt->left);
        int n = getMin(bt->right);
        if(bt->left&&!bt->right)//右子树不存在则不一定是最小高度
            return m+1;
        if(bt->right&&!bt->left)
            return n+1;
        int result = min(n,m)+1;//左右子树都存在则返回相对小的树高
        return result;
    }

    int minDepth(TreeNode* root) {
        return getMin(root);
    }
};

6.7完全二叉树的结点

class Solution {
public:
    int countNodes(TreeNode* root) {
        if(!root) return 0;
        return 1+countNodes(root->left)+countNodes(root->right);
    }
};

6.8平衡二叉树

class Solution {
public:
    int getHigh(TreeNode* node){
        if(!node) return 0;
        int leftheight = getHigh(node->left);
        if(leftheight == -1) return -1;
        int rightheight = getHigh(node->right);
        if(rightheight == -1) return -1;
        return abs(leftheight-rightheight)>1?-1:1+max(leftheight,rightheight);//左右子树绝对值之差超过1则返回-1，否则返回当前树高
    }


    bool isBalanced(TreeNode* root) {
        int result = getHigh(root);
        return result==-1?false:true;
    }
};

6.9二叉树的所有路径

class Solution {
private:
    void getPath(TreeNode* bt,vector<int>& path,vector<string>& result){
        path.push_back(bt->val);
        if(!bt->left&&!bt->right){//访问到叶子结点才出手
            string spath;
            for(int i = 0;i<path.size()-1;i++){
                spath += to_string(path[i]);//path路径的值除了叶子结点赋值给spath（强制转换）
                spath += "->";
            }
            spath += to_string(path[(path.size()-1)]);//叶子结点值入路径
            result.push_back(spath);
            return;
        }
        if(bt->left){
            getPath(bt->left,path,result);
            path.pop_back();//只有向上回溯才会pop
        }
        if(bt->right){
            getPath(bt->right,path,result);
            path.pop_back();
        }
    }

public:
    vector<string> binaryTreePaths(TreeNode* root) {
        vector<string> result;
        vector<int> path;
        if(!root) return result;
        getPath(root,path,result);
        return result;
    }
};