把二叉搜索树转换为累加树
1.题目
2.自己初解的思路及问题
略,直接看力扣题解
3.题解方法一:反中序遍历
class Solution {
int sum = 0;
public TreeNode convertBST(TreeNode root) {
if (root != null) {
convertBST(root.right);
sum += root.val;
root.val = sum;
convertBST(root.left);
}
return root;
}
}
4.题解方法二:Morris 遍历
class Solution {
public TreeNode convertBST(TreeNode root) {
int sum = 0;
TreeNode node = root;
while (node != null) {
if (node.right == null) {
sum += node.val;
node.val = sum;
node = node.left;
} else {
TreeNode succ = getSuccessor(node);
if (succ.left == null) {
succ.left = node;
node = node.right;
} else {
succ.left = null;
sum += node.val;
node.val = sum;
node = node.left;
}
}
}
return root;
}
public TreeNode getSuccessor(TreeNode node) {
TreeNode succ = node.right;
while (succ.left != null && succ.left != node) {
succ = succ.left;
}
return succ;
}
}