📚 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));