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IncreasingBST897.java
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IncreasingBST897.java
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package Leetcode;
import java.util.ArrayList;
import java.util.Deque;
import java.util.LinkedList;
import java.util.List;
public class IncreasingBST897 {
/**Method: InOrder; Time: O(N); Space: O(N) **/
/**
对其进行「中序遍历」即可得到有序列表,再根据有序列表构建答案即可。
**/
List<TreeNode> res = new ArrayList<>();
public TreeNode increasingBST(TreeNode root) {
bfs(root);
return getNode();
}
private TreeNode getNode() {
TreeNode dummy = new TreeNode();
TreeNode cur = dummy;
for(TreeNode node:res ){
cur.right = node;
node.left = null; //注意:left == null;
cur = node;
}
return dummy.right;
}
// Method 1: BFS
private void bfs(TreeNode node) {
Deque<TreeNode> q = new LinkedList<>();
while(node != null || !q.isEmpty()) {
while(node != null) {
q.add(node);
node = node.left;
}
node = q.pollLast();
res.add(node);
node = node.right;
}
}
// Method 2: DFS
private void dfs(TreeNode node) {
if(node == null) {
return;
}
dfs(node.left);
res.add(node);
dfs(node.right);
}
//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;
}
}
}