Given a Binary Tree of size N , where each node can have positive or negative values. Convert this to a tree where each node contains the sum of the left and right sub trees of the original tree. The values of leaf nodes are changed to 0.
Example 1:
Input:
10
/ \
-2 6
/ \ / \
8 -4 7 5
Output:
20
/ \
4 12
/ \ / \
0 0 0 0
Explanation:
(4-2+12+6)
/ \
(8-4) (7+5)
/ \ / \
0 0 0 0

Your Task:
You dont need to read input or print anything. Complete the function toSumTree() which takes root node as input parameter and modifies the given tree in-place.
Note: If you click on Compile and Test the output will be the in-order traversal of the modified tree.
Expected Time Complexity: O(N)
Expected Auxiliary Space: O(height of tree)

Constraints:
1 ≤ N ≤ 10^{4}

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