447. Number of Boomerangs#2(Done)

Solution#2

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;}

Solution#1

Problem#1

• map的用法，getOrDefault(key, default)，遍历方法, map.clear()