leetcode112.路径总和

解法1是DFS，解法2是BFS
DFS应用了前序遍历的方法，BFS用的层序遍历求和，qt表示用队列存储树节点指针，qi表示存储到该节点的路径和

class Solution {
public:
    bool hasPathSum(TreeNode* root, int targetSum) {
        if(!root){
            return false;
        }
        bool flag=false;
        bool& exist=flag;
        // dfs(root,0,targetSum,exist);
        bfs(root,targetSum,exist);
        return exist;
    }
    void dfs(TreeNode* tn,int sum,int targetSum,bool& exist){
        if(!tn){
            return;
        }
        sum+=tn->val;
        if(sum==targetSum&&!tn->left&&!tn->right){
            exist=true;
            return;
        }
        dfs(tn->left,sum,targetSum,exist);
        dfs(tn->right,sum,targetSum,exist);
    }
    void bfs(TreeNode*node,int targetSum,bool& exist){
        if(!node){
            return;
        }
        if(!node->left&&!node->right){
            exist=targetSum==node->val;
        }
        queue<TreeNode*> qt;
        queue<int> qi;
        qt.push(node);
        qi.push(node->val);
        while(!qt.empty()){
            int sz=qt.size();
            for(int i=0;i<sz;++i){
                TreeNode* tn=qt.front();
                int sum=qi.front();
                if(tn->left){
                    int sum1=tn->left->val+sum;
                    if(!tn->left->left&&!tn->left->right&&sum1==targetSum){
                        exist=true;
                        return;
                    }
                    qt.push(tn->left);
                    qi.push(sum1);
                }
                if(tn->right){
                    int sum1=tn->right->val+sum;
                    if(!tn->right->left&&!tn->right->right&&sum1==targetSum){
                        exist=true;
                        return;
                    }
                    qt.push(tn->right);
                    qi.push(sum1);

                }
                qt.pop();
                qi.pop();
            }
        }
    }
};
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