<p>You are given the <code>root</code> of a <strong>binary tree</strong> with <code>n</code> nodes. Each node is uniquely assigned a value from <code>1</code> to <code>n</code>. You are also given an integer <code>startValue</code> representing the value of the start node <code>s</code>, and a different integer <code>destValue</code> representing the value of the destination node <code>t</code>.</p>

<p>Find the <strong>shortest path</strong> starting from node <code>s</code> and ending at node <code>t</code>. Generate step-by-step directions of such path as a string consisting of only the <strong>uppercase</strong> letters <code>&#39;L&#39;</code>, <code>&#39;R&#39;</code>, and <code>&#39;U&#39;</code>. Each letter indicates a specific direction:</p>

<ul>
	<li><code>&#39;L&#39;</code> means to go from a node to its <strong>left child</strong> node.</li>
	<li><code>&#39;R&#39;</code> means to go from a node to its <strong>right child</strong> node.</li>
	<li><code>&#39;U&#39;</code> means to go from a node to its <strong>parent</strong> node.</li>
</ul>

<p>Return <em>the step-by-step directions of the <strong>shortest path</strong> from node </em><code>s</code><em> to node</em> <code>t</code>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2021/11/15/eg1.png" style="width: 214px; height: 163px;" />
<pre>
<strong>Input:</strong> root = [5,1,2,3,null,6,4], startValue = 3, destValue = 6
<strong>Output:</strong> &quot;UURL&quot;
<strong>Explanation:</strong> The shortest path is: 3 &rarr; 1 &rarr; 5 &rarr; 2 &rarr; 6.
</pre>

<p><strong class="example">Example 2:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2021/11/15/eg2.png" style="width: 74px; height: 102px;" />
<pre>
<strong>Input:</strong> root = [2,1], startValue = 2, destValue = 1
<strong>Output:</strong> &quot;L&quot;
<strong>Explanation:</strong> The shortest path is: 2 &rarr; 1.
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li>The number of nodes in the tree is <code>n</code>.</li>
	<li><code>2 &lt;= n &lt;= 10<sup>5</sup></code></li>
	<li><code>1 &lt;= Node.val &lt;= n</code></li>
	<li>All the values in the tree are <strong>unique</strong>.</li>
	<li><code>1 &lt;= startValue, destValue &lt;= n</code></li>
	<li><code>startValue != destValue</code></li>
</ul>

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    void parentmap(TreeNode* root,TreeNode* parent,unordered_map<int,TreeNode*>&mp,int &cnt, TreeNode* &temp,int &startValue){
        if(root==NULL) return;
        mp[root->val]=parent;
        if(root->val==startValue){
            temp=root;
        }
        cnt++;
        if(root->left){
            parentmap(root->left,root,mp,cnt,temp,startValue);
        }
        if(root->right){
             parentmap(root->right,root,mp,cnt,temp,startValue);
        }

    }
    void dfs(TreeNode* temp,string &ans,vector<int>&vis,unordered_map<int,TreeNode*>&mp,int &destValue,string &fans){
        vis[temp->val]=1;
        if(temp->val==destValue) {
            if(fans.length()==0) fans=ans;
            else if(ans.length()<fans.length()) fans=ans;
            return;
        }
        if(temp->left){
            if(vis[temp->left->val]==0)
            {ans+='L';
            dfs(temp->left,ans,vis,mp,destValue,fans);
            ans.pop_back();}
        }
        if(temp->right){
            if(vis[temp->right->val]==0)
            {ans+='R';
            dfs(temp->right,ans,vis,mp,destValue,fans);
            ans.pop_back();}
        }
        if(mp[temp->val]!=NULL){
            if(vis[mp[temp->val]->val]==0){
              ans+='U';
            dfs(mp[temp->val],ans,vis,mp,destValue,fans);
            ans.pop_back();
            }
        }
        
    }
    string getDirections(TreeNode* root, int startValue, int destValue) {
       unordered_map<int,TreeNode*>mp;
       int cnt=1;
       TreeNode* temp=NULL;
       parentmap(root,NULL,mp,cnt,temp, startValue);
       vector<int>vis(cnt+1,0);
       vis[startValue]=1;
       string ans="";
       string fans="";
       dfs(temp,ans,vis,mp,destValue,fans);
       return fans;
       



       
       
    }
};
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