https://leetcode.com/problems/construct-string-from-binary-tree/description/
struct TreeNode {
int val;
TreeNode *left;
TreeNode *right;
TreeNode(int x) : val(x), left(NULL), right(NULL) {}
};
class Solution {
public:
string tree2str(TreeNode* t) {
string s;
if(t==NULL) return "";
s += to_string(t->val);
if(t->left != NULL){
s+="("+tree2str(t->left)+")";
}
if((t->left==NULL)&&(t->right!=NULL)){
s+="()";
}
if(t->right!=NULL)
s+= "("+tree2str(t->right)+")";
return s;
}
};