Path Sum II

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Path Sum II

Given a binary tree and a sum, find all root-to-leaf paths where each path’s sum equals the given sum.

For example:

Given the below binary tree and sum = 22,

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5
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7
      5
     / \
    4   8
   /   / \
  11  13  4
 /  \    / \
7    2  5   1

return

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[
   [5,4,11,2],
   [5,8,4,5]
]

DFS+回溯。

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/**
 * 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:

    vector<int> vi;
    vector<vector<int>> vvi;

    void DFS(TreeNode* root, int sum)
    {
        if (root == NULL) return;
        if (root->left == NULL && root->right == NULL)
        {
            if (sum == root->val)
            {
                vi.push_back(root->val);
                vvi.push_back(vi);
                vi.pop_back();
            }
            return;
        }
        vi.push_back(root->val);
        sum -= root->val;
        DFS(root->left,sum);
        DFS(root->right,sum);
        vi.pop_back();
    }

    vector<vector<int>> pathSum(TreeNode* root, int sum) {
        DFS(root,sum);
        return vvi;
    }
};