02-线性结构4 Pop Sequence (25分)

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 51 2 3 4 5 6 73 2 1 7 5 6 47 6 5 4 3 2 15 6 4 3 7 2 11 7 6 5 4 3 2

Sample Output:

YESNONOYESNO

解：这题通过pop的结果推测push的顺序，判断是否能够pop出该结果。在check_stack中主要判断三个条件满足才能进行push操作，具体见代码：

#include <iostream>#include <stdlib.h>using namespace std;#define maxlen 1000typedef struct node{int data[maxlen];int capacity;int top;}stack;int M,N,K;stack *create_stack(){stack *ptr = (stack*)malloc(sizeof(struct node));ptr->capacity = maxlen;ptr->top = -1;return ptr;}void push(stack *ptr, int num){if(ptr->top == ptr->capacity -1){cout<<"Full";return;}ptr->top++;ptr->data[ptr->top] = num;}int top(stack *ptr){return ptr->data[ptr->top];}void pop(stack *ptr){if(ptr->top == -1){cout<<"Empty";return;}ptr->top--;}int check_stack(int data[]){int capacity = M+1;stack *ptr = create_stack();push(ptr,0);int index = 0;int num = 1;while(index != N){while(top(ptr)<data[index] && ptr->top+1 < capacity && index != N){push(ptr,num++);}if(top(ptr) == data[index]){pop(ptr);index++;}elsereturn false;}return true;}int main(){cin>>M>>N>>K;int dat[N];int i;for(;K!=0;--K){for(i = 0; i < N; i++){cin>>dat[i];}if(check_stack(dat)){cout<<"YES"<<endl;}else{cout<<"NO"<<endl;}}return 0;}

2017-4-16 待续