package com.example.lettcode.offer;

import java.util.Stack;

/**
 * @Class ValidateStackSequences
 * @Description 劍指offer 31 棧的壓入、彈出序列
 * 輸入兩個整數序列，第一個序列表示棧的壓入順序，請判斷第二個序列是否為該棧的彈出順序。
 * 假設壓入棧的所有數字均不相等。例如，序列 {1,2,3,4,5} 是某棧
 * 的壓棧序列，序列 {4,5,3,2,1} 是該壓棧序列對應的一個彈出序列，
 * 但 {4,3,5,1,2} 就不可能是該壓棧序列的彈出序列。
 * <p>
 * 示例 1：
 * 輸入：pushed = [1,2,3,4,5], popped = [4,5,3,2,1]
 * 輸出：true
 * 解釋：我們可以按以下順序執行：
 * push(1), push(2), push(3), push(4), pop() -> 4,
 * push(5), pop() -> 5, pop() -> 3, pop() -> 2, pop() -> 1
 * <p>
 * 示例 2：
 * 輸入：pushed = [1,2,3,4,5], popped = [4,3,5,1,2]
 * 輸出：false
 * 解釋：1 不能在 2 之前彈出。
 * <p>
 * 提示：
 * 0 <= pushed.length == popped.length <= 1000
 * 0 <= pushed[i], popped[i] < 1000
 * pushed 是 popped 的排列。
 * @Author
 * @Date 2020/7/17
 **/
public class ValidateStackSequences {
    // 使用輔助棧
    public static boolean validateStackSequences(int[] pushed, int[] popped) {
        if (pushed.length != popped.length) return false;

        Stack<Integer> integerStack = new Stack<>();
        int locationFirst = 0;
        int locationSecond = 0;
        while (locationFirst < pushed.length && locationSecond < popped.length) {
            // 棧為空或者棧頂元素與poped 當前元素不相同,則pushed元素入棧
            while (integerStack.isEmpty()
                    || (locationFirst < pushed.length && integerStack.peek() != popped[locationSecond])) {
                integerStack.push(pushed[locationFirst]);
                locationFirst++;
            }
            // 棧頂元素和poped當前元素相等則棧頂出棧
            while (!integerStack.isEmpty()
                    && locationSecond < popped.length
                    && integerStack.peek() == popped[locationSecond]) {
                integerStack.pop();
                locationSecond++;
            }
        }

        // 結束迴圈，判斷兩指標是否均指向最後一個元素的位置，即是否相等
        return locationFirst == locationSecond;
    }

    public static void main(String[] args) {
        int[] pushed = new int[]{1, 2, 3, 4, 5};
        int[] poped = new int[]{4, 5, 3, 2, 1};
        boolean ans = validateStackSequences(pushed, poped);
        System.out.println("ValidateStackSequences demo01 result:" + ans);

        pushed = new int[]{1, 2, 3, 4, 5};
        poped = new int[]{4, 3, 5, 1, 2};
        ans = validateStackSequences(pushed, poped);
        System.out.println("ValidateStackSequences demo02 result:" + ans);
    }
}