596.Minimum Subtree

1.Description(Easy)

Given a binary tree, find the subtree with minimum sum. Return the root of the subtree.

Example

Given a binary tree:

     1
   /   \
 -5     2
 / \   /  \
0   2 -4  -5

return the node1.

2.Code

与597 Subtree with maximum average 相似，

两个类变量 TreeNode 记录当前变量，minsum记录变化的最小值

 public TreeNode node=null;
 public int minsum=Integer.MAX_VALUE;
 public TreeNode findSubtree(TreeNode root){
     helper(root);
     return node;
 }
 public int helper(TreeNode root){
     if(root==null){
         return 0;
     }
     int left=helper(root.left);
     int right=helper(root.right);
        int sum=root.val+left+right;
        if(sum<minsum){
            minsum=sum;
            node=root;
        }
        return sum;
 }