面试题33. 二叉搜索树的后序遍历序列¶
Tags: Medium
Tree
Links: https://leetcode-cn.com/problems/er-cha-sou-suo-shu-de-hou-xu-bian-li-xu-lie-lcof/
输入一个整数数组,判断该数组是不是某二叉搜索树的后序遍历结果。如果是则返回 true,否则返回 false。假设输入的数组的任意两个数字都互不相同。
参考以下这颗二叉搜索树:
5
/ \
2 6
/ \
1 3
示例 1:
输入: [1,6,3,2,5]
输出: false
示例 2:
输入: [1,3,2,6,5]
输出: true
提示:
数组长度 <= 1000
class Solution {
public:
bool verifyPostorder(vector<int>& postorder) {
std::ios_base::sync_with_stdio(false);
cin.tie(NULL);
cout.tie(NULL);
if (postorder.size() <= 2) return true;
return verifyPostorder(postorder, 0, postorder.size() - 1);
}
bool verifyPostorder(vector<int> & v, int left, int right)
{
int root = v[right];
int pos = left;
//搜索左子树部分
while (pos < right) {
if (v[pos] > root) break;
else ++pos;
}
//验证右子树
int r = pos;
while (r < right) {
if (v[r] < root) return false;
else ++r;
}
bool flag_l = true, flag_r = true;
if (pos > left) flag_l = verifyPostorder(v, left, pos - 1);
if (pos < right) flag_r = verifyPostorder(v, pos, right - 1);
return flag_l && flag_r;
}
};