题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=5929
题意：维护一个栈，支持往栈里塞 0/1 ，弹栈顶，翻转栈，询问从栈底到栈顶按顺序 NAND 的值。
题解：只要知道最后的 00 后面 11 的个数的奇偶性就行。可以用链表把所有 00 的位置存下来。
1 #include <bits/stdc++.h> 2 using namespace std; 3 4 typedef long long LL; 5 6 const int maxn = 866666; 7 int n; 8 int q[maxn], l, r; 9 int ll[maxn], rr[maxn]; 10 int zerol, zeror; 11 char cmd[10]; 12 13 int main() { 14 // freopen("in", "r", stdin); 15 int T, _ = 1; 16 scanf("%d", &T); 17 while(T--) { 18 scanf("%d", &n); 19 l = maxn/2 + 1; r = maxn/2; 20 int x, cur; 21 zerol = zeror = -1; 22 int dir = 0, zero = 0; 23 printf("Case #%d: ", _++); 24 while(n--) { 25 scanf("%s", cmd); 26 if(strcmp(cmd, "PUSH")==0) { 27 scanf("%d", &x); 28 if(!dir) { 29 q[--l] = x; 30 cur = l; 31 } 32 else { 33 q[++r] = x; 34 cur = r; 35 } 36 if(x == 0) { 37 zero++; 38 if(zero == 1) { 39 zerol = zeror = cur; 40 ll[cur] = rr[cur] = -1; 41 } 42 else { 43 if(!dir) { 44 ll[zerol] = cur; rr[cur] = zerol; 45 ll[cur] = -1; zerol = cur; 46 } 47 else { 48 rr[zeror] = cur; ll[cur] = zeror; 49 rr[cur] = -1; zeror = cur; 50 } 51 } 52 } 53 } 54 if(strcmp(cmd, "POP")==0) { 55 if(!dir) { 56 x = q[l]; 57 cur = l++; 58 } 59 else { 60 x = q[r]; 61 cur = r--; 62 } 63 if(x == 0) { 64 zero--; 65 if(zero == 0) zerol = zeror = -1; 66 else { 67 if(!dir) { 68 ll[rr[cur]] = -1; 69 zerol = rr[cur]; 70 } 71 else { 72 rr[ll[cur]] = -1; 73 zeror = ll[cur]; 74 } 75 } 76 } 77 } 78 else if(strcmp(cmd, "REVERSE")==0) dir ^= 1; 79 else if(strcmp(cmd, "QUERY")==0) { 80 int siz = r - l + 1, one; 81 if(!siz) printf("Invalid. "); 82 else { 83 if(!zero) printf("%d ", siz%2); 84 else { 85 int tmp; 86 if(!dir) { 87 one = r - zeror; 88 tmp = (zeror == l); 89 } 90 else { 91 one = zerol - l; 92 tmp = (zerol == r); 93 } 94 printf("%d ", one % 2 == tmp); 95 } 96 } 97 } 98 } 99 } 100 return 0; 101 }