2017.2.18[codevs1170]NOIP2008提高组复赛T4双栈排序

体面不贴

这题一开始卡了我好久……策了好久贪心都判断不了无解情况……

直到看了题解才发现自己有多傻逼……

传送门：http://blog.csdn.net/kqzxcmh/article/details/9566813

题解写的很清楚这里就不赘述了。

两次AC，还行吧。

关键是我太蒟蒻……

 1 #include<cstdio>
 2 #include<cstdlib>
 3 #include<cstring>
 4 #include<iostream>
 5 #include<algorithm>
 6 #define N 1010
 7 #define RG register
 8 #define inf 0x3f3f3f3f
 9 using namespace std;
10 char ans[N];
11 bool mat[N][N];
12 int n,top1,top2,top,topo,inn[N],col[N],dp[N],sta1[N],sta2[N];
13 inline int Min(RG const int &a,RG const int &b){return a>b?b:a;}
14 inline int gi(){
15     RG int x=0;RG char c=getchar();
16     while(c<‘0‘||c>‘9‘) c=getchar();
17     while(c>=‘0‘&&c<=‘9‘) x=x*10+c-‘0‘,c=getchar();
18     return x;
19 }
20 inline bool dfs(RG int now){
21     for (RG int i=1;i<=n;++i)
22     if(mat[now][i]){
23         if(!col[i]){
24         col[i]=3-col[now];
25         if(!dfs(i)) return 0;
26         }
27         else if(col[i]==col[now])
28                 return 0;
29     }
30     return 1;
31 }
32 inline void out(){
33     ++topo;
34     if(sta1[top1]==topo&&top1){
35     ans[++top]=‘b‘;
36     --top1;
37     }
38     else{
39     ans[++top]=‘d‘;
40     --top2;
41     }
42 }
43 inline void work(){
44     n=gi();dp[n+1]=sta1[0]=sta2[0]=inf;
45     for (RG int i=1;i<=n;++i) inn[i]=gi();
46     for (RG int i=n;i>=1;--i) dp[i]=Min(dp[i+1],inn[i]);
47     for (RG int i=1;i<n-1;++i)
48     for (RG int j=i+1;j<n;++j)
49         if(inn[j]>inn[i]&&dp[j+1]<inn[i])
50         mat[i][j]=mat[j][i]=1;
51     for (RG int i=1;i<=n;++i)
52     if(!col[i]){
53         col[i]=1;
54         if(!dfs(i)){
55         printf("0\n");
56         return;
57         }
58     }
59     for (RG int i=1;i<=n;++i){
60     if(col[i]<2){
61         while(inn[i]>sta1[top1]) out();
62         ans[++top]=‘a‘;
63         sta1[++top1]=inn[i];
64     }
65     else{
66         while(sta1[top1]==topo+1&&top1){
67             ans[++top]=‘b‘;
68             --top1;
69         ++topo;
70             }
71         while(inn[i]>sta2[top2]) out();
72         ans[++top]=‘c‘;
73         sta2[++top2]=inn[i];
74     }
75     }
76     while(top1||top2) out();
77     for (RG int i=1;i<=top;++i) printf("%c ",ans[i]);
78     putchar(‘\n‘);
79 }
80 int main(){
81     freopen("3114.in","r",stdin);
82     freopen("3114.out","w",stdout);
83     work();
84     fclose(stdin);
85     fclose(stdout);
86     return 0;
87 }