力扣------路径总和 III

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     struct TreeNode *left;
 *     struct TreeNode *right;
 * };
 */
int count;
void sum(struct TreeNode* root, int targetSum,long int nowsum){
    if(nowsum==targetSum){
        count++;
    }
    if(root->left){
        nowsum=nowsum+root->left->val;
        sum(root->left,targetSum,nowsum);
        nowsum=nowsum-root->left->val;
    }
    if(root->right){
        nowsum=nowsum+root->right->val;
        sum(root->right,targetSum,nowsum);
        nowsum=nowsum-root->right->val;       
    }
}
void dfs(struct TreeNode* root, int targetSum){
    long int nowsum=0;
    nowsum=nowsum+root->val;
    sum(root, targetSum,nowsum);
    if(root->left){
        dfs(root->left,targetSum);
    }
    if(root->right){
        dfs(root->right,targetSum);
    }
}
int pathSum(struct TreeNode* root, int targetSum){
    count=0;
    if(!root){
        return count;
    }
    dfs(root,targetSum);
    return count;
}
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