GuilinDev
Lc0404
05 August 2008
代码
如何判断是左叶子结点，用一个flag的topdown传递下去
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/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode() {}
* TreeNode(int val) { this.val = val; }
* TreeNode(int val, TreeNode left, TreeNode right) {
* this.val = val;
* this.left = left;
* this.right = right;
* }
* }
*/
class Solution {
int result;
public int sumOfLeftLeaves(TreeNode root) {
result = 0;
dfs(root, false);
return result;
}
private void dfs(TreeNode node, boolean isLeft) {
if (node == null) {
return;
}
if (node.left == null && node.right == null && isLeft) {
result += node.val;
}
dfs(node.left, true);
dfs(node.right, false);
}
}
网上的做法，向下判断两层
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class Solution {
/*
https://leetcode.com/problems/sum-of-left-leaves/discuss/88950/Java-iterative-and-recursive-solutions
*/
public int sumOfLeftLeaves(TreeNode root) {
//Recursive，从最深的叶子开始加
if (root == null) {
return 0;
}
int ans = 0;
if (root.left != null) {
if (root.left.left == null && root.left.right == null) {//到底了
ans += root.left.val;
} else {
ans += sumOfLeftLeaves(root.left);
}
}
ans += sumOfLeftLeaves(root.right);
return ans;
}
/*
//Iterative
public int sumOfLeftLeaves(TreeNode root) {
if(root == null) return 0;
int ans = 0;
Stack<TreeNode> stack = new Stack<TreeNode>();
stack.push(root);
while(!stack.empty()) {
TreeNode node = stack.pop();
if(node.left != null) {
if (node.left.left == null && node.left.right == null)
ans += node.left.val;
else
stack.push(node.left);
}
if(node.right != null) {
if (node.right.left != null || node.right.right != null)
stack.push(node.right);
}
}
return ans;
}
*/
}