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.
题目含义：获取所有左叶子节点的总和
方法一：
1 public int sumOfLeftLeaves(TreeNode root) { 2 if (root == null) return 0; 3 int ans = 0; 4 if (root.left != null) { 5 if (root.left.left == null && root.left.right == null) ans += root.left.val; 6 else ans += sumOfLeftLeaves(root.left); 7 } 8 ans += sumOfLeftLeaves(root.right); 9 return ans; 10 }
方法二：
1 public int sumOfLeftLeaves(TreeNode root) { 2 if (root == null) return 0; 3 int ans = 0; 4 Stack<TreeNode> stack = new Stack<TreeNode>(); 5 stack.push(root); 6 while (!stack.empty()) { 7 TreeNode node = stack.pop(); 8 if (node.left != null) { 9 if (node.left.left == null && node.left.right == null) ans += node.left.val; 10 else stack.push(node.left); 11 } 12 if (node.right != null) { 13 if (node.right.left == null && node.right.right == null) continue; 14 else stack.push(node.right); 15 } 16 } 17 return ans; 18 }