Leetcode 112. Path Sum

Whether there is a root-to-leaf node and equals the given number. Idea: Recursion. Determine if the left son or right son exists this path (sum becomes sum-root->val). Ver0: Recursion to the end will be the left and right son of the leaf node, so to have root==null judgment

1 classSolution {2  Public:3     BOOLHaspathsum (treenode* root,intsum) {4         if(root==NULL) {//error5             if(Sum = =0)return true;6             Else return false;7         }8         //if (sum < root->val) return false;9         returnHaspathsum (root->left,sum-root->val) | | Haspathsum (root->right,sum-root->val);Ten     } One};

WA:

Input:[] 0 Output:true expected:false Ver1: Whether the original tree is empty additionally judged.

1 classSolution {2  Public:3     BOOLHaspathsum (treenode* root,intsum) {4         if(Root==null)return false;5         returnHelp (root,sum);6         7     }8     9     BOOLHelp (treenode* root,intsum) {Ten         if(root==NULL) { One             if(Sum = =0)return true; A             Else return false; -         } -         //if (sum < root->val) return false; the         returnHelp (root->left,sum-root->val) | | Help (root->right,sum-root->val);//error -     } -};

WA:

Input:[1] Output:true expected:false mistakenly treats only one son's node as a leaf node. Ver2:

1 classSolution {2  Public:3     BOOLHaspathsum (treenode* root,intsum) {4         if(Root==null)return false;5         returnHelp (root,sum);6         7     }8     9     BOOLHelp (treenode* root,intsum) {Ten         if(root==NULL) { One             if(Sum = =0)return true; A             Else return false; -         } -         //if (sum < root->val) return false; the          -         if(Root->left && root->right)returnHelp (root->left,sum-root->val) | | Help (root->right,sum-root->val); -         if(Root->left)returnHelp (root->left,sum-root->val); -         if(Root->right)returnHelp (root->right,sum-root->val);

Leaf-node: +         if(Sum = =0)return true;//error -         return false; +          A     } at};

WA:

Input:[1] 1 Output:false expected:true in the case of a leaf node, the error is judged (i.e. sum==0) and should be sum==root->val. Ver3:

1 classSolution {2  Public:3     BOOLHaspathsum (treenode* root,intsum) {4         if(Root==null)return false;5         returnHelp (root,sum);6         7     }8     9     BOOLHelp (treenode* root,intsum) {Ten         //if (root==null) { One         //if (sum = = 0) return true; A         //else return false; -         // } -         //if (sum < root->val) return false; the          -         if(Root->left && root->right)returnHelp (root->left,sum-root->val) | | Help (root->right,sum-root->val); -         if(Root->left)returnHelp (root->left,sum-root->val); -         if(Root->right)returnHelp (root->right,sum-root->val); +         if(sum = = Root->val)return true; -         return false; +          A     } at};

other people's concise version of the code:

1 classSolution {2  Public:3     BOOLHaspathsum (treenode* root,intsum) {4         if(root==NULL)5             return false;6         if(Root->val = = Sum && root->left = = NULL && Root->right = =NULL)7             return true;8         returnHaspathsum (Root->left, sum-root->val) | | Haspathsum (Root->right, sum-root->val);9     }Ten};

Recursive to the last pass is the leaf node, not its left and right son, so there is no need to open the Help function.

If it is a node with only one son, it can also be processed (within the judgment of Root==null).

Leetcode 112. Path Sum