1051 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 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
题解:模拟入队出队操作
#include<bits/stdc++.h> using namespace std; const int maxn=100010; stack<int> st; int m,n,k; int num[maxn]; bool isSeq(){ while(st.size()>0){//清空前一次栈内元素 st.pop(); } int k=0; for(int i=1;i<=n;i++){ if(st.size()>=m){ return false; } st.push(i); while(st.top()==num[k]){ st.pop(); k++; if(st.size()==0){//一定要判断,否则不能执行st.top()语句 break; } } } if(st.size()>=1){ return false; } else{ return true; } } int main(){ scanf("%d %d %d",&m,&n,&k); for(int i=0;i<k;i++){ for(int j=0;j<n;j++){ scanf("%d",&num[j]); } if(isSeq()){ printf("YES\n"); } else{ printf("NO\n"); } } return 0; }
优化代码:
#include<bits/stdc++.h> using namespace std; const int maxn=100010; int m,n,k; vector<int> v; bool isSeq(){ stack<int> st; int k=0; for(int i=1;i<=n;i++){ if(st.size()>=m){ return false; } st.push(i); while(!st.empty()&&st.top()==v[k]){ st.pop(); k++; } } if(st.size()>=1){ return false; } else{ return true; } } int main(){ scanf("%d %d %d",&m,&n,&k); v.resize(n+1); for(int i=0;i<k;i++){ v.clear(); for(int j=0;j<n;j++){ scanf("%d",&v[j]);//注意:vector<> v 在没有初始化大小时,不能使用该语句赋值,只能使用push_back() } if(isSeq()){ printf("YES\n"); } else{ printf("NO\n"); } } return 0; }