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AtCoder Regular Contest 069 D

D - Menagerie

Time limit : 2sec / Memory limit : 256MB

Score : 500 points

Problem Statement

Snuke, who loves animals, built a zoo.

There are N animals in this zoo. They are conveniently numbered 1 through N, and arranged in a circle. The animal numbered i(2≤i≤N−1) is adjacent to the animals numbered i−1 and i+1. Also, the animal numbered 1 is adjacent to the animals numbered 2 and N, and the animal numbered N is adjacent to the animals numbered N−1 and 1.

There are two kinds of animals in this zoo: honest sheep that only speak the truth, and lying wolves that only tell lies.

Snuke cannot tell the difference between these two species, and asked each animal the following question: "Are your neighbors of the same species?" The animal numbered i answered s_i. Here, if s_i is o, the animal said that the two neighboring animals are of the same species, and if s_i is x, the animal said that the two neighboring animals are of different species.

More formally, a sheep answered o if the two neighboring animals are both sheep or both wolves, and answered x otherwise. Similarly, a wolf answered x if the two neighboring animals are both sheep or both wolves, and answered o otherwise.

Snuke is wondering whether there is a valid assignment of species to the animals that is consistent with these responses. If there is such an assignment, show one such assignment. Otherwise, print -1.

Constraints

3≤N≤10⁵
s is a string of length N consisting of o and x.

Input

The input is given from Standard Input in the following format:

N
s

Output

If there does not exist an valid assignment that is consistent with s, print -1. Otherwise, print an string t in the following format. The output is considered correct if the assignment described by t is consistent with s.

t is a string of length N consisting of S and W.
If t_i is S, it indicates that the animal numbered i is a sheep. If t_i is W, it indicates that the animal numbered i is a wolf.

Sample Input 1

6
ooxoox

Sample Output 1

SSSWWS

For example, if the animals numbered 1, 2, 3, 4, 5 and 6 are respectively a sheep, sheep, sheep, wolf, wolf, and sheep, it is consistent with their responses. Besides, there is another valid assignment of species: a wolf, sheep, wolf, sheep, wolf and wolf.

Let us remind you: if the neiboring animals are of the same species, a sheep answers o and a wolf answers x. If the neiboring animals are of different species, a sheep answers x and a wolf answers o.

Sample Input 2

3
oox

Sample Output 2

-1

Print -1 if there is no valid assignment of species.

Sample Input 3

10
oxooxoxoox

Sample Output 3

SSWWSSSWWS

题目链接：http://arc069.contest.atcoder.jp/tasks/arc069_b

题意：n只动物从1到n围成一个圈，每只动物要么是羊要么是狼。每只动物会说出一个字母，说'o'表示它两边动物种类相同，说'x'表示不同。但羊是说真话，狼是说反话。求出这n只动物的种类。

分析：模拟一下就可以了，不过这个模拟比较大！

下面给出AC代码：

  1 #include <bits/stdc++.h>
  2 using namespace std;
  3 const int N=123456;
  4 int gh(char *str,char *ch,int n) {
  5     for(int i=1; i<n; i++) {
  6         if(i<n-2) {
  7             if(str[i]=='o') {
  8                 if(ch[i]=='S') {
  9                     ch[i+1]=ch[i-1];
 10                 } else {
 11                     if(ch[i-1]=='S') ch[i+1]='W';
 12                     else ch[i+1]='S';
 13                 }
 14             } else {
 15                 if(ch[i]=='S') {
 16                     if(ch[i-1]=='S') ch[i+1]='W';
 17                     else ch[i+1]='S';
 18                 } else {
 19                     ch[i+1]=ch[i-1];
 20                 }
 21             }
 22         }
 23         else if(i==n-2) {
 24             if(str[i]=='o') {
 25                 if(ch[i]=='S') {
 26                     if(ch[i+1]!=ch[i-1]) {
 27                         return 1;
 28                     }
 29                 }
 30                 else {
 31                     if(ch[i+1]==ch[i-1]){
 32                         return 1;
 33                     }
 34                 }
 35             }
 36             else{
 37                 if(ch[i]=='S'){
 38                     if(ch[i+1]==ch[i-1]){
 39                         return 1;
 40                     }
 41                 }
 42                 else{
 43                     if(ch[i+1]!=ch[i-1]) {
 44                         return 1;
 45                     }
 46                 }
 47             }
 48         }
 49         else if(i==n-1){
 50             if(str[i]=='x'){
 51                 if(ch[i]=='S') {
 52                     if(ch[n-2]==ch[0]) return 1;
 53                 }
 54                 else{
 55                     if(ch[n-2]!=ch[0]) return 1;
 56                 }
 57             }
 58             else{
 59                 if(ch[i]=='S'){
 60                     if(ch[n-2]!=ch[0]) return 1;
 61                 }
 62                 else{
 63                     if(ch[n-2]==ch[0]) return 1;
 64                 }
 65             }
 66         }
 67     }
 68     return 0;
 69 }
 70 int main() {
 71     char str[N];
 72     char ch[N];
 73     int n;
 74     int flag=0;
 75     scanf("%d",&n);
 76     scanf("%s",str);
 77     ch[0]='S';
 78     if(str[0]=='o') {
 79         memset(ch,0,sizeof(ch));
 80         ch[0]='S';
 81         ch[1]='S';
 82         ch[n-1]='S';
 83         flag=gh(str,ch,n);
 84         if(flag==0) {
 85             for(int i=0; i<n; i++) printf("%c",ch[i]);
 86             puts("");
 87             return 0;
 88         } else {
 89             memset(ch,0,sizeof(ch));
 90             ch[0]='S';
 91             ch[1]='W';
 92             ch[n-1]='W';
 93             flag=gh(str,ch,n);
 94             if(flag==0){
 95                 for(int i=0;i<n;i++) printf("%c",ch[i]);
 96                 puts("");
 97                 return 0;
 98             }
 99         }
100     }
101     else{
102         memset(ch,0,sizeof(ch));
103         ch[0]='S';
104         ch[1]='S';
105         ch[n-1]='W';
106         flag=gh(str,ch,n);
107         if(flag==0){
108             for(int i=0;i<n;i++) printf("%c",ch[i]);
109             puts("");
110             return 0;
111         }
112         else{
113             memset(ch,0,sizeof(ch));
114             ch[0]='S';
115             ch[1]='W';
116             ch[n-1]='S';
117             flag=gh(str,ch,n);
118             if(flag==0){
119                 for(int i=0;i<n;i++) printf("%c",ch[i]);
120                 puts("");
121                 return 0;
122             }
123         }
124     }
125     ch[0]='W';
126     if(str[0]=='o'){
127         memset(ch,0,sizeof(ch));
128         ch[0]='W';
129         ch[1]='S';
130         ch[n-1]='W';
131         flag=gh(str,ch,n);
132         if(flag==0){
133             for(int i=0;i<n;i++) printf("%c",ch[i]);
134             puts("");
135             return 0;
136         }
137         else{
138             ch[0]='W';
139             ch[1]='W';
140             ch[n-1]='S';
141             flag=gh(str,ch,n);
142             if(flag==0){
143                 for(int i=0;i<n;i++) printf("%c",ch[i]);
144                 puts("");
145                 return 0;
146             }
147         }
148     }
149     else{
150         memset(ch,0,sizeof(ch));
151         ch[0]='W';
152         ch[1]='S';
153         ch[n-1]='S';
154         flag=gh(str,ch,n);
155         if(flag==0){
156             for(int i=0;i<n;i++) printf("%c",ch[i]);
157             puts("");
158         }
159         else{
160             ch[0]='W';
161             ch[1]='W';
162             ch[n-1]='W';
163             flag=gh(str,ch,n);
164             if(flag==0){
165                 for(int i=0;i<n;i++) printf("%c",ch[i]);
166                 puts("");
167                 return 0;
168             }
169         }
170     }
171     puts("-1");
172     return 0;
173 }

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原文地址：https://www.cnblogs.com/ECJTUACM-873284962/p/6502115.html