255. Verify Preorder Sequence in Binary Search Tree

Topic:

Given An array of numbers, verify whether it is the correct preorder traversal sequence of a binary search tree.

Assume each of the sequence is unique.

Follow up:
Could does it using only constant space complexity?

Links: http://leetcode.com/problems/verify-preorder-sequence-in-binary-search-tree/

Exercises

Use stack to simulate preorder traversal, mid, left, right. The main code is a reference to Stefan Pochmann's solution.

Time Complexity-o (n), Space Complexity-o (LOGN)

 Public classSolution { Public BooleanVerifypreorder (int[] preorder) {        intLow =Integer.min_value; Stack<Integer> stack =NewStack<>();  for(intI:preorder) {            if(I <Low )return false;  while(!stack.isempty () && i >Stack.peek ()) Low=Stack.pop ();        Stack.push (i); }                return true; }}

No solution using Stack,space complexity O (1), using the original array

 Public classSolution { Public BooleanVerifypreorder (int[] preorder) {        intLow = integer.min_value, index =-1;  for(intI:preorder) {            if(I <Low )return false;  while(Index >= 0 && i >Preorder[index]) Low= preorder[index--]; preorder[++index] =i; }                return true; }}

Reference:

Https://leetcode.com/discuss/51543/java-o-n-and-o-1-extra-space

Https://leetcode.com/discuss/52060/72ms-c-solution-using-one-stack-o-n-time-and-space

Https://leetcode.com/discuss/65241/ac-python-o-n-time-o-1-extra-space

Https://leetcode.com/discuss/68862/my-c-solution-easy-to-understand

255. Verify Preorder Sequence in Binary Search Tree