PROBLEM DESCRIPTION
Given the root of a binary tree, return all root-to-leaf paths in any order. A leaf is a node with no children.
SOLUTION
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class Solution {
public List<String> binaryTreePaths(TreeNode root) {
pathHelper(root, new ArrayList<String>());
return convertToListOfString(ans);
}
List<List<String>> ans = new ArrayList<List<String>>();
public void pathHelper(TreeNode root, List<String> list){
if(root == null){
return;
}
//pre-order traversal
list.add(root.val + "");
pathHelper(root.left, list);
pathHelper(root.right, list);
//if leaf node, add to anser list
if(root.left == null && root.right == null){
ans.add(new ArrayList<String>(list));
}
//backtrack
list.remove(list.size()-1);
}
public List<String> convertToListOfString(List<List<String>> list){
List<String> ans = new ArrayList<>();
StringBuffer sb = new StringBuffer();
for(int i=0; i<list.size(); i++){
List<String> t = list.get(i);
for(int j=0; j<t.size(); j++){
sb.append(t.get(j) + "->");
}
ans.add(new String(sb.toString().substring(0, sb.length()-2)));
sb = new StringBuffer();
}
return ans;
}
}