1051. Pop Sequence (25) 出栈序列的合法性

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.

Input Specification:

Each input file contains one test case. For each case, the first line contains 3 numbers (all no more than 1000): M (the maximum capacity of the stack), N (the length of push sequence), and K (the number of pop sequences to be checked). Then K lines follow, each contains a pop sequence of N numbers. All the numbers in a line are separated by a space.

Output Specification:

For each pop sequence, print in one line "YES" if it is indeed a possible pop sequence of the stack, or "NO" if not.

Sample Input:

5 7 5
1 2 3 4 5 6 7
3 2 1 7 5 6 4
7 6 5 4 3 2 1
5 6 4 3 7 2 1
1 7 6 5 4 3 2

Sample Output:

YES
NO
NO
YES
NO

考察栈。

代码：

#include <stdio.h>

int main() {
    int m,n,k,s[1000],c,d,num,flag;
    scanf("%d%d%d",&m,&n,&k);
    while(k --) {
        c = num = flag = 0;
        for(int i = 0;i < n;i ++) {
            scanf("%d",&d);
            if(!c || s[c - 1] != d)
                while(c < m && (s[c ++] = ++ num) != d);
            if(s[c - 1] != d) flag = 1;
            else c --;
        }
        if(flag) printf("NO
");
        else printf("YES
");
    }
    return 0;
}