Pop Sequence

這是PAT上的一道題，用c++簡單些，因爲要用到堆棧（stack), 我用c語言寫了個， 如果有簡單的思路， 希望大家提示

#include<stdio.h>
#include<stdlib.h>
#define MAX 1000
int a[MAX];
typedef struct SNode{
	int *m;
	int top;
} *Stack;
void Push(Stack PtrS, int x);
void Pop(Stack PtrS);
Stack createStack()
{
	Stack PtrS = (Stack)malloc(sizeof(struct SNode));
	PtrS->m = (int *)malloc(sizeof(int)*MAX);
	PtrS->top = -1;
	
	return PtrS;
}
int main()
{	
	
	int M, N, K, start, flag;
	scanf("%d%d%d", &M, &N, &K);
	Stack PtrS = createStack();	// 一個堆棧
	while(K--)	// 3 2 1 7 5 6 4

	{	start = 0; flag = 1;
		for(int i = 0; i < N; i++)
			scanf("%d", &a[i]); 	// 讀入一組數據
			//printf("test\n");
		PtrS->top = -1;
		for(int i = 0; i < N; i++)
		{	//printf("test\n");
		if(PtrS->m[PtrS->top] > a[i] && PtrS->top != -1)
			{
				flag = 0; break;
			}
		
		
		
			if(PtrS->top == -1 || PtrS->m[PtrS->top] < a[i])
			{		//printf("test\n");
				for(int j = start+1; j <= a[i] && PtrS->top < M-1; j++)
				{
					Push(PtrS, j); start++;	
				}		
			}
			if(PtrS->top == M-1 && PtrS->m[PtrS->top] != a[i])
			{
				 flag = 0; break;
			}
			Pop(PtrS);							
		 } 
		 
		 printf("%s\n", flag == 1 ? "YES" : "NO");
	 } 
	
	return 0;
}
// 進棧
void Push(Stack PtrS, int x)
{
	if(PtrS->top == MAX-1)
		return;
	PtrS->m[++PtrS->top] = x;
 } 
// 出棧
void Pop(Stack PtrS)
{
	if(PtrS->top == -1)
		return;
	 PtrS->top--;
 }