二叉树中最小级别的所有叶节点的总和

      1
     / \
    2   3
   / \   \
  4   5   6

// 二叉树节点定义
class TreeNode {
  constructor(val) {
    this.val = val;
    this.left = null;
    this.right = null;
  }
}

// 计算二叉树中最小级别的所有叶节点的总和
function calculateMinLevelLeafSum(root) {
  if (root === null) {
    return 0;
  }
  
  let queue = [root];
  let sum = 0;
  
  while (queue.length > 0) {
    let levelSize = queue.length;
    
    for (let i = 0; i < levelSize; i++) {
      let node = queue.shift();
      
      if (node.left === null && node.right === null) {
        sum += node.val;
      }
      
      if (node.left !== null) {
        queue.push(node.left);
      }
      
      if (node.right !== null) {
        queue.push(node.right);
      }
    }
  }
  
  return sum;
}

// 创建示例二叉树
let root = new TreeNode(1);
root.left = new TreeNode(2);
root.right = new TreeNode(3);
root.left.left = new TreeNode(4);
root.left.right = new TreeNode(5);
root.right.right = new TreeNode(6);

// 计算最小级别的所有叶节点的总和
let minLevelLeafSum = calculateMinLevelLeafSum(root);
console.log(minLevelLeafSum); // 输出：15