404. Sum of Left Leaves

404. Sum of Left Leaves

1. 题目

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.

2. 题解：

• 解题思路： 递归函数中借助一个变量来标记左右孩子。如果为左孩子，且为叶子结点，则加上此节点的值；如果有节点存在，则遍历右子树
• 代码实现：

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     struct TreeNode *left;
 *     struct TreeNode *right;
 * };
 */
#define RIGHT_CHILD 0
#define LEFT_CHILD  1
int sumOfLeftLeavesRecursion(struct TreeNode* root, int child){
    if(NULL == root){
        return 0;
    }
    if(NULL == root->left && NULL == root->right && LEFT_CHILD == child)
        return root->val;
    
    return sumOfLeftLeavesRecursion(root->left, LEFT_CHILD) + sumOfLeftLeavesRecursion(root->right, RIGHT_CHILD); 
}


int sumOfLeftLeaves(struct TreeNode* root){
    if(NULL == root){
        return 0;
    }
    return sumOfLeftLeavesRecursion(root, RIGHT_CHILD);/*根节点需要输出吗???  leetcode结果显示不需要*/
}

• 提交结果：