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  • [LC] 404. Sum of Left Leaves

    Find the sum of all left leaves in a given binary tree.

    Example:

        3
       / 
      9  20
        /  
       15   7
    
    There are two left leaves in the binary tree, with values 9 and 15 respectively. Return 24.

    Solution 1:
    BFS
    /**
     * Definition for a binary tree node.
     * public class TreeNode {
     *     int val;
     *     TreeNode left;
     *     TreeNode right;
     *     TreeNode(int x) { val = x; }
     * }
     */
    class Solution {
        public int sumOfLeftLeaves(TreeNode root) {
            int res = 0;
            if (root == null) {
                return res;
            }
            Queue<TreeNode> queue = new LinkedList<>();
            queue.offer(root);
            while (!queue.isEmpty()) {
                TreeNode cur = queue.poll();
                if (cur.left != null) {
                    if (cur.left.left == null && cur.left.right == null) {
                        res += cur.left.val;
                    } else {
                        queue.add(cur.left);
                    }
                }
                if (cur.right != null) {
                    queue.add(cur.right);
                }
            }
            return res;
        }
    }


    Solution 2:
    DFS
    /**
     * Definition for a binary tree node.
     * public class TreeNode {
     *     int val;
     *     TreeNode left;
     *     TreeNode right;
     *     TreeNode(int x) { val = x; }
     * }
     */
    class Solution {
        public int sumOfLeftLeaves(TreeNode root) {
            if (root == null) {
                return 0;
            }
            int res = 0;
            if (root.left != null) {
                if (root.left.left == null && root.left.right == null) {
                    res += root.left.val;
                } else {
                    res += sumOfLeftLeaves(root.left);
                }
            }
            res += sumOfLeftLeaves(root.right);
            return res;
        }
    }
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  • 原文地址:https://www.cnblogs.com/xuanlu/p/12148649.html
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