例题6-2 铁轨（Rails, ACM/ICPC CERC 1997, UVa 514）

#include <iostream>#include <string>#include <vector>#include <stack>#include <queue>#include <deque>#include <set>#include <map>#include <algorithm>#include <sstream>#include <utility>#include <cstring>#include <cstdio>#include <cstdlib>#include <cmath>#include <cctype>#define CLEAR(a, b) memset(a, b, sizeof(a))#define IN() freopen("in.txt", "r", stdin)#define OUT() freopen("out.txt", "w", stdout)const int maxn = 1000005;using LL = long long;using UI = unsigned int;const int mod = 1e6 + 7;using namespace std;//------------------------------------------------------------------------------------------//int q[1005] = { 0 }, rear = 0, front = 0;int s[1005] = { 0 }, sfront = 0;bool judge(int x) {if (x >= q[rear] && front != rear) {//若出栈的数大于等于队首的数，则应当把数入栈，当然队列空了也要考虑while (q[rear] != x) s[sfront++] = q[rear++];//把到x为止的所有数入栈，出队rear++;//x出队，入栈出栈}else {if (s[--sfront] != x) return false;//比较栈顶元素与出栈元素}return true;}int main() {#ifdef _DEBUGIN(); OUT();#endifint N;while (cin >> N && N) {int x;while (cin >> x && x) {bool flag = true;CLEAR(q, 0), rear = 0, front = 0;CLEAR(s, 0), sfront = 0;for (int i = 1; i <= N; i++) q[front++] = i;//入队if (!judge(x)) flag = false;for (int i = 0; i < N - 1; ++i) {scanf("%d", &x);if (!judge(x)) flag = false;}if (flag) cout << "Yes\n";else cout << "No\n";}cout << endl;}return 0;}//参考了lls的代码int a[1005];int main() {#ifdef _DEBUGIN(); OUT();#endifint n;while (cin >> n && n) {while (cin >> a[1] && a[1]) {stack<int> s;bool flag = true;for (int i = 2; i <= n; ++i) cin >> a[i];int A = 1, B = 1;//定义A,B两个类似指针的变量来比较，值得学习。while (B != n) {//这个循环把情况全考虑了，，，好厉害啊。。if (A == a[B]) A++, B++;else if (!s.empty() && s.top() == a[B]) s.pop(), B++;else if (A < a[B]) s.push(A++);else { flag = false; break; }}if (flag) cout << "Yes" << endl;else cout << "No" << endl;}cout << endl;}return 0;}