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leetcode404. sum of left leaves

admin 11月 13, 2020 0

累加二叉树所有左叶子节点的值。

404. Sum of Left Leaves

Find the sum of all left leaves in a given binary tree.

Example:

    3
   / 
  9  20
    /  
   15   7

There are two left leaves in the binary tree, with values 9 and 15 respectively. Return 24.

算法：基于前序遍历算法，判断一个叶子节点是否是左叶子节点，然后累加。

public int sum = 0;
public int (TreeNode root) {
    if (root != null) preorderWalk(root);
    return sum;
}
public void preorderWalk(TreeNode root) {
    if (root == null) return;
    if (root.left != null) {
        if (root.left.right == null && root.left.left == null) sum += root.left.val;
    }
    preorderWalk(root.left);
    preorderWalk(root.right);
}