Gym 101190F Foreign Postcards

题意和转移就不讲了，讲讲比较 迷 的一点吧。

比赛结束之前，WA好多遍也没过，，

我开始还以为状态转移不对，或者写搓了，但是队友坚持查错，最终发现了这些有趣的地方。

目前只能怀疑和编译器有关系。

这样写是正确的，可以AC：

dp[0][0]=s[0]=='C'?1:0;

这样写是不行的，27组测试数据处会WA：

(s[0]=='C')?dp[0][0]=1:dp[0][0]=0;

还有，if{}else{}也不行，27组测试数据处会WA：

    if (s[0]=='C') {        dp[0][0]=1.0;    } else {        dp[0][0]=0.0;    }

先贴上AC代码：

#include<map>#include<set>#include<list>#include<stack>#include<deque>#include<queue>#include<vector>#include<sstream>#include<iomanip>#include<iostream>#include<math.h>#include<ctype.h>#include<stdio.h>#include<stdlib.h>#include<string.h>#include<algorithm>#include<functional>#define CPY(A,B)memcpy(A,B,sizeof(A))#define fin freopen("in.txt","r",stdin)#define fout freopen("out.txt","w",stdout)typedef long long LL;typedef unsigned long long uLL;const int MOD=1e9+7;const int INF=0x3f3f3f3f;const LL INFF=0x3f3f3f3f3f3f3f3fLL;const double OO=1e20;const double EPS=1e-9;const double PI=acos (-1.0);int dx[]= {0,1,0,-1};int dy[]= {1,0,-1,0};using namespace std;int gcd (const LL &a,const LL &b) {    return b==0?a:gcd (b,a%b);}inline int dcmp (double a,double b) {    if (fabs (a-b) <EPS) { return 0; }    return a>b;}const int M=1e6+50;double dp[M][2];string s;int ss;bool judge (int n) {    return s[n]=='C'?true:false;}void Init() {    cin>>s;    ss=s.size();//    if (judge (0) ) {//        dp[0][0]=1.0;//        dp[0][1]=0.0;//    } else {//        dp[0][0]=0.0;//        dp[0][1]=1.0;//    }}int main() {    freopen ("foreign.in","r",stdin);    freopen ("foreign.out","w",stdout);    Init();    dp[0][0]=s[0]=='C'?1:0;    dp[0][1]=s[0]=='C'?0:1;    double p,ans=0.0;    for (int i=1; i<ss; ++i) {        p=1.0/ (ss+1-i);//        dp[i][0]= (1.0-p) *dp[i-1][0];//        if (judge (i) ) {//            dp[i][0]+=p;//        }        dp[i][0]=judge (i) ? (p+ (1-p) *dp[i-1][0]) : ( (1-p) * dp[i-1][0]);        dp[i][1]=1.0-dp[i][0];        (judge (i) ) ?ans+=dp[i][1]:ans+=dp[i][0];    }    printf ("%.10f\n",ans);    return 0;}

WA在第27组的代码：

#include<map>#include<set>#include<list>#include<stack>#include<deque>#include<queue>#include<vector>#include<sstream>#include<iomanip>#include<iostream>#include<math.h>#include<ctype.h>#include<stdio.h>#include<stdlib.h>#include<string.h>#include<algorithm>#include<functional>#define CPY(A,B)memcpy(A,B,sizeof(A))#define fin freopen("in.txt","r",stdin)#define fout freopen("out.txt","w",stdout)typedef long long LL;typedef unsigned long long uLL;const int MOD=1e9+7;const int INF=0x3f3f3f3f;const LL INFF=0x3f3f3f3f3f3f3f3fLL;const double OO=1e20;const double EPS=1e-9;const double PI=acos (-1.0);int dx[]= {0,1,0,-1};int dy[]= {1,0,-1,0};using namespace std;int gcd (const LL &a,const LL &b) {    return b==0?a:gcd (b,a%b);}inline int dcmp (double a,double b) {    if (fabs (a-b) <EPS) { return 0; }    return a>b;}const int M=1e6+50;double dp[M][2];string s;int ss;bool judge (int n) {    return s[n]=='C'?true:false;}void Init() {    cin>>s;    ss=s.size();    if (judge (0) ) {        dp[0][0]=1.0;        dp[0][1]=0.0;    } else {        dp[0][0]=0.0;        dp[0][1]=1.0;    }//这样用if和else会WA}int main() {    freopen ("foreign.in","r",stdin);    freopen ("foreign.out","w",stdout);    Init();    double p,ans=0.0;    for (int i=1; i<ss; ++i) {        p=1.0/ (ss+1-i);        dp[i][0]= (1.0-p) *dp[i-1][0];        if (judge (i) ) {            dp[i][0]+=p;        }//这里用if也会WA        //judge (i) ?dp[i][0]=(p+ (1-p) *dp[i-1][0]) :dp[i][0]=( (1-p) * dp[i-1][0]);//这样写，也会WA        dp[i][1]=1.0-dp[i][0];        (judge (i) ) ?ans+=dp[i][1]:ans+=dp[i][0];    }    printf ("%.10f\n",ans);    return 0;}