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📚 11.左叶子之和

💻 代码实现

typescript
/**
 * @url https://leetcode.cn/problems/sum-of-left-leaves/description/
 */

class TreeNode {
  val: number;
  left: TreeNode | null;
  right: TreeNode | null;
  constructor(val?: number, left?: TreeNode | null, right?: TreeNode | null) {
    this.val = val === undefined ? 0 : val;
    this.left = left === undefined ? null : left;
    this.right = right === undefined ? null : right;
  }
}

function sumOfLeftLeaves(root: TreeNode | null): number {
  let sum = 0;
  const dfs = (root: TreeNode | null | undefined) => {
    if (!root) return;
    if (root.left && !root.left.left && !root.left.right) {
      sum += root.left.val;
      // return
      // PS:notice:这里容易return掉
    }
    dfs(root.left);
    dfs(root.right);
  };
  dfs(root);
  return sum;
}

// ;[3, 9, 20, null, null, 15, 7]

let root = new TreeNode(
  3,
  new TreeNode(9),
  new TreeNode(20, new TreeNode(15), new TreeNode(7))
);
console.log(sumOfLeftLeaves(root));

Released under the MIT License.