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a_671.java
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27 lines (26 loc) · 965 Bytes
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package datastructure.tree;
/**
* 找出二叉树中第二小的节点
*/
public class a_671 {
//思想：递归从左子树找出第二小结点，从右子树找出第二小结点
//比较左右子树第二小结点大小，取较小的一方，
//返回-1表示没找到
public int findSecondMinimumValue(TreeNode root) {
if (root == null) return -1;
if (root.left == null && root.right == null) return -1;
int leftVal = root.left.val;
int rightVal = root.right.val;
if (root.val == leftVal) leftVal = findSecondMinimumValue(root.left);
if (root.val == rightVal) rightVal = findSecondMinimumValue(root.right);
if (leftVal != -1 && rightVal != -1) return Math.min(leftVal, rightVal);
if (leftVal != -1) return leftVal;
return rightVal;
}
class TreeNode {
int val;
TreeNode left;
TreeNode right;
TreeNode(int x) { val = x; }
}
}