?LeetCode刷題實(shí)戰(zhàn)404：左葉子之和

class?Solution?{
public:

????void helper(TreeNode* root,int& sum,bool is_left){
????????if(root==NULL){//空節(jié)點(diǎn)返回
????????????return;
????????}
????????//為葉子結(jié)點(diǎn)
????????if(root->left==NULL&&root->right==NULL){
????????????if(is_left){//為左結(jié)點(diǎn)
????????????????sum+=root->val;
????????????}
????????????return;
????????}
????????helper(root->left,sum,true);//遍歷左子樹，標(biāo)識(shí)是左子樹
????????helper(root->right,sum,false);//遍歷右子樹，標(biāo)識(shí)不是左子樹
????}

????int sumOfLeftLeaves(TreeNode* root) {
??????//處理特殊的情形
????????if(root==NULL||(root->left==NULL&&root->right==NULL)){
????????????return?0;
????????}
????????int sum=0;
????????helper(root,sum,true);
????????return?sum;
????}
};