中序遍历Java版

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/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public int getMinimumDifference(TreeNode root) {
        TreeNode pre = null, cur = root;
        Stack s = new Stack();
        int min = Integer.MAX_VALUE;

        
        while(s.isEmpty() == false || cur != null) {
            while(cur != null) {
                s.push(cur);
                cur = cur.left;
            }

            if(s.isEmpty() == false) {
                cur = s.peek();
                if(pre != null) {
                    int dis = cur.val - pre.val;
                    if(dis < min)
                        min = dis;
                }

                s.pop();
                pre = cur;
                cur = cur.right;
            }

        }

        return min;
    }
}