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SumNumbers.java
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package Algorithms.tree;
import java.util.ArrayList;
/*
*
* Sum Root to Leaf Numbers Total Accepted: 23940 Total Submissions: 80436 My Submissions
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.
* */
public class SumNumbers {
public int sumNumbers(TreeNode root) {
if (root == null) {
return 0;
}
ArrayList<Integer> ret = new ArrayList<Integer>();
// 存储从根节点到当前节点的路径上的数字
ArrayList<Integer> path = new ArrayList<Integer>();
dfs(root, path, ret);
int sum = 0;
for (int n: ret) {
sum += n;
}
return sum;
}
public void dfs(TreeNode root, ArrayList<Integer> path, ArrayList<Integer> ret) {
if (root == null) {
return;
}
path.add(root.val);
if (root.left == null && root.right == null) {
int num = 0;
for (int n: path) {
num = num * 10 + n;
}
ret.add(num);
} else {
// 向左右子树递归
dfs(root.left, path, ret);
dfs(root.right, path, ret);
}
// 一定要记得回溯，也就是说递归不能修改Path本身，否则以上向左右子树分别递归时 path就会被改。
path.remove(path.size() - 1);
}
}