leetcode 86: Sum Root to Leaf Numbers
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Sum Root to Leaf Numbers2 days
Given a binary tree containing digits from 0-9 only, each root-to-leaf path could represent a number.
An example is the root-to-leaf path 1->2->3 which represents the number 123.
Find the total sum of all root-to-leaf numbers.
For example,
1 / \ 2 3
The root-to-leaf path 1->2 represents the number 12.
The root-to-leaf path 1->3 represents the number 13.
Return the sum = 12 + 13 = 25.
/** * Definition for binary tree * struct TreeNode { * int val; * TreeNode *left; * TreeNode *right; * TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */class Solution {public: int sumNumbers(TreeNode *root) { // Start typing your C/C++ solution below // DO NOT write int main() function if(root==NULL) return 0; return sumRec(root, 0); } private: int sumRec(TreeNode *root, int presum) { int x = presum*10 + root->val; if(root->left==NULL && root->right==NULL) { return x; } if(root->left==NULL) { return sumRec(root->right, x); } if(root->right==NULL) { return sumRec(root->left, x); } return sumRec(root->left, x) + sumRec(root->right, x); }};wrong try. bottom up. should use top bottom
/** * Definition for binary tree * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode(int x) { val = x; } * } */public class Solution { public int sumNumbers(TreeNode root) { // Start typing your Java solution below // DO NOT write main() function if(root==null) return 0; Pair pair = sumRec( root); return pair.first; } private Pair sumRec(TreeNode root) { if(root==null) { return new Pair(-1,0); } Pair left = sumRec(root.left); Pair right = sumRec(root.right); int x = root.val; int l = 0, r=0; if(left.first!=-1) { l = (int)(root.val * Math.pow(10,left.second)) + left.first; } else { l = 0; } if(right.first !=-1) { r = (int)(root.val * Math.pow(10,right.second)) + right.first; } else { r = 0; } return new Pair( l+r, (left.second>right.second ? left.second+1 : right.second+1) ); } static class Pair{ public int first; public int second; public Pair(int x, int y) {first=x; second=y;} }}correct one:
/** * Definition for binary tree * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode(int x) { val = x; } * } */public class Solution { public int sumNumbers(TreeNode root) { // Start typing your Java solution below // DO NOT write main() function return sumRec(root, 0); } private int sumRec(TreeNode root, int num) { if(root==null) { return 0; } num = num*10 + root.val; int left=0, right=0; if(root.left!=null) left = sumRec(root.left, num); if(root.right!=null) right = sumRec(root.right, num); int res = left + right; return res==0? num : res; }}final version:
/** * Definition for binary tree * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode(int x) { val = x; } * } */public class Solution { public int sumNumbers(TreeNode root) { // Start typing your Java solution below // DO NOT write main() function if(root==null) return 0; return sumRec(root, 0) ; } private int sumRec(TreeNode root, int parentSum) { int x = parentSum*10 + root.val; int l=0, r=0; if(root.left!=null) { l = sumRec(root.left, x); } if(root.right!=null) { r = sumRec(root.right, x); } if( l==0 && r==0) return x; else return l+r; }}
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