leetcode-437-Path Sum III

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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.

Example:

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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
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//dfs
public class Solution {
    public int pathSum(TreeNode root, int sum) {
        if(root == null)
            return 0;
        return findPath(root, sum) + pathSum(root.left, sum) + pathSum(root.right, sum);
    }
    
    public int findPath(TreeNode root, int sum){
        int res = 0;
        if(root == null)
            return res;
        if(sum == root.val)
            res++;
        res += findPath(root.left, sum - root.val);
        res += findPath(root.right, sum - root.val);
        return res;
    }
   
}
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