堆栈

判断输入的序列是否可以从确定栈中得到
Given a stack which can keep M numbers at most. Push N numbers in the order of 1, 2, 3, ...,

N and pop randomly. You are supposed to tell if a given sequence of numbers is a possible

pop sequence of the stack. For example, if M is 5 and N is 7, we can obtain 1, 2, 3, 4, 5, 6, 7

from the stack, but not 3, 2, 1, 7, 5, 6, 4.

import java.util.*;

class stack{
 int Max;
 int data[];
 int top=-1;
 public stack(int M) {
  this.Max = M;
  data = new int[Max];
 }
 public void push(int item) {
  if(top == Max-1) {
  // System.out.println("O");
  }
  else {
   data[++top] = item;
  }
 }
 public int pop() {
  if(top == -1) {
   return -1;
  }
  else {
   return data[top--];
  }
 }
}
public class Main { 
 public static void main(String[] args) {
 Scanner in = new Scanner(System.in);
 int max = in.nextInt();
 
 int num =in.nextInt();
 int[] n = new int[num];
 int K = in.nextInt();
 
 for(int k = K; k>0; k--) {
  int p = 1;
  int last=0;
  stack s = new stack(max);
  for(int i = 0; i<num; i++) {
   n[i] = in.nextInt();
  }
  
  loop:
  {  
   for(int i = 0; i<num; i++) {
    while(p<=n[i]) {
     if(s.top == s.Max-1) {
      System.out.println("NO");
      break loop;
     }
     s.push(p);
     last = p;
     p++;
    } 
    if(n[i]==last) {
     if(s.pop()==-1) {
      System.out.println("NO");
      break loop;
     }
     if(s.top!=-1) {
      last = s.data[s.top];
     }
    }
    else {
     System.out.println("NO");
           break loop;
    }
   }
   System.out.println("YES");
  } 
 }
 in.close();
 }

}

（竟然一次过！可能方法刚好和题目要考察的一些特殊情况匹配。）