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package com.ltaocs.stack;

import java.util.Stack;

/**

* Lin Tao

* a.ltaocs.com

* LeetCode 946 Validate Stack Sequences

* Given two sequences pushed and popped with distinct values, return true if and only if this could have been the result of a sequence of push and pop operations on an initially empty stack.

* Example 1:

* Input: pushed = [1,2,3,4,5], popped = [4,5,3,2,1]

* Output: true

* Explanation: We might do the following sequence:

* push(1), push(2), push(3), push(4), pop() -> 4,

* push(5), pop() -> 5, pop() -> 3, pop() -> 2, pop() -> 1

* Example 2:

* Input: pushed = [1,2,3,4,5], popped = [4,3,5,1,2]

* Output: false

* Explanation: 1 cannot be popped before 2.

* Note:

* 0 <= pushed.length == popped.length <= 1000

* 0 <= pushed[i], popped[i] < 1000

* pushed is a permutation of popped.

* pushed and popped have distinct values.

*/

public class ValidateStackSequences {

public boolean validateStackSequences(int[] pushed, int[] popped) {

int poppedPoint = 0;

Stack<Integer> stack = new Stack<>();

for (int i = 0; i < pushed.length; i++) {

if (pushed[i] != popped[poppedPoint]) {

stack.push(pushed[i]);

} else {

poppedPoint++;

while (!stack.empty() && stack.peek() == popped[poppedPoint]) {

poppedPoint++;

stack.pop();

}

}

}

for (int i = poppedPoint; i < popped.length; i++) {

if (!stack.empty()) {

int pop = stack.pop();

if (pop != popped[poppedPoint]) {

return false;

} else {

poppedPoint++;

}

}

}

return stack.empty() ? true : false;

}

public static void main(String[] args) {

int[] pushed = {1, 2, 3, 4, 5};

int[] popped = {4, 5, 3, 2, 1};

int[] pushed1 = {2, 1, 0};

int[] popped1 = {1, 2, 0};

ValidateStackSequences v = new ValidateStackSequences();

System.out.println(v.validateStackSequences(pushed1, popped1));

}

}