Path Sum III问题及解法
2017-04-18 15:36
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问题描述:
You are given a binary tree in which each node contains an integer value.
Find the number of paths that sum to a given value.
The path does not need to start or end at the root or a leaf, but it must go downwards (traveling only from parent nodes to child nodes).
The tree has no more than 1,000 nodes and the values are in the range -1,000,000 to 1,000,000.
示例:
问题分析:
求解树上某一段连续路径的和是否等于给定值,然后求出这些路径的得数目。可以考虑利用DFS求解。
过程详见代码:
/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
int temp;
int pathSum(TreeNode* root, int sum) {
temp = sum;
if(root == NULL) return 0;
return pathSum2(root,sum) + pathSum(root->left,sum) + pathSum(root->right,sum);
}
int pathSum2(TreeNode* root, int sum)
{
int res = 0;
if(root == NULL) return 0;
if(root->val == sum) res = 1;
return res + pathSum2(root->left,sum - root->val) + pathSum2(root->right,sum - root->val);
}
};
You are given a binary tree in which each node contains an integer value.
Find the number of paths that sum to a given value.
The path does not need to start or end at the root or a leaf, but it must go downwards (traveling only from parent nodes to child nodes).
The tree has no more than 1,000 nodes and the values are in the range -1,000,000 to 1,000,000.
示例:
root = [10,5,-3,3,2,null,11,3,-2,null,1], sum = 8 10 / \ 5 -3 / \ \ 3 2 11 / \ \ 3 -2 1 Return 3. The paths that sum to 8 are: 1. 5 -> 3 2. 5 -> 2 -> 1 3. -3 -> 11
问题分析:
求解树上某一段连续路径的和是否等于给定值,然后求出这些路径的得数目。可以考虑利用DFS求解。
过程详见代码:
/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
int temp;
int pathSum(TreeNode* root, int sum) {
temp = sum;
if(root == NULL) return 0;
return pathSum2(root,sum) + pathSum(root->left,sum) + pathSum(root->right,sum);
}
int pathSum2(TreeNode* root, int sum)
{
int res = 0;
if(root == NULL) return 0;
if(root->val == sum) res = 1;
return res + pathSum2(root->left,sum - root->val) + pathSum2(root->right,sum - root->val);
}
};
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