左叶子之和

Author: mayuanucas

README.md

@@ -130,6 +130,7 @@
 | 377 | 动态规划 | [组合总和 Ⅳ](src/main/java/algorithm/leetcode/Solution377.java) | 中等 |
 | 392 | 动态规划、贪心算法、二分查找 | [判断子序列](src/main/java/algorithm/leetcode/Solution392.java) | 中等 |
 | 402 | 栈、贪心算法 | [移掉K位数字](src/main/java/algorithm/leetcode/Solution402.java) | 中等 |
+| 404 | 树 | [左叶子之和](src/main/java/algorithm/leetcode/Solution404.java) | 简单 |
 | 406 | 贪心算法 | [根据身高重建队列](src/main/java/algorithm/leetcode/Solution406.java) | 中等 |
 | 413 | 数学、动态规划 | [等差数列划分](src/main/java/algorithm/leetcode/Solution413.java) | 中等 |
 | 416 | 动态规划 | [分割等和子集](src/main/java/algorithm/leetcode/Solution416.java) | 中等 |

src/main/java/algorithm/leetcode/Solution404.java

@@ -0,0 +1,38 @@
+package algorithm.leetcode;
+
+/**
+ * @author: mayuan
+ * @desc: 左叶子之和
+ * @date: 2019/03/10
+ */
+public class Solution404 {
+ public int sumOfLeftLeaves(TreeNode root) {
+ if (null == root){
+ return 0;
+ }
+
+ return dfs(root.left, true) + dfs(root.right, false);
+ }
+
+ private int dfs(TreeNode node, boolean isLeft) {
+ if (null == node) {
+ return 0;
+ }
+
+ if (null == node.left && null == node.right && isLeft) {
+ return node.val;
+ } else {
+ return dfs(node.left, true) + dfs(node.right, false);
+ }
+ }
+
+ public class TreeNode {
+ int val;
+ TreeNode left;
+ TreeNode right;
+
+ TreeNode(int x) {
+ val = x;
+ }
+ }
+}