Tree Sum of left leaves

Execution time limit is 1 second

Runtime memory usage limit is 128 megabytes

Given a binary tree. Find the sum of all its left leaves.

Definition of a tree:

// Java
class TreeNode
{
public:
  int val;
  TreeNode left;
  TreeNode right;
  TreeNode(int x) {
    val = x;
    left = NULL; 
    right = NULL;
};

// C++
class TreeNode
{
public:
  int val;
  TreeNode *left;
  TreeNode *right;
  TreeNode(int x) : val(x), left(NULL), right(NULL) {}
};

Implement a function sumLeft that returns the sum of left leaves in the tree. If input tree haven't left leaves, return $0$ .

// Java
int sumLeft(TreeNode tree)

// C++
int sumLeft(TreeNode *tree)

Note

Function sumLeft returns $14 = 5 + 9$ .

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