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  • Codeforces 305E Playing with String

    传送门:http://codeforces.com/problemset/problem/305/E

    思路:首先每个字符都可选的子串可以看成一个独立的游戏,那么最终的答案就可以通过所有独立游戏的SG值的异或和得到。


    代码:

    #include<cstdio>
    #include<cstring>
    #include<algorithm>
    const int n=5010;
    using namespace std;
    int sg[n];char s[n];bool bo[n];
    
    int getsg(int len){
    	if (sg[len]!=-1) return sg[len];
    	memset(bo,0,sizeof(bo));
    	bo[getsg(len-2)]=1;
    	for (int i=1;i+i<len;i++) bo[getsg(i-1)^getsg(len-i-2)]=1;
    	for (int i=0;i<n;i++) if (!bo[i]) return sg[len]=i;
    }
    
    int getans(int l,int r){
    	int sum=0;
    	for (int i=l+1;i<=r-1;i++) 
    		if (s[i+1]==s[i-1]){
    			int len=0;
    			while (s[i+1]==s[i-1]&&i<=r-1) i++,len++;
    			sum^=sg[len];
    			printf("%d
    ",len);
    		}
    	return sum;
    }
    
    int main(){
    	memset(sg,-1,sizeof(sg));
    	sg[0]=0,sg[1]=1;
    	for (int i=2;i<n;i++) if (sg[i]==-1) sg[i]=getsg(i);
    	for (int i=0;i<=10;i++) { printf("%d",sg[i]); }
    	while (scanf("%s",s)!=EOF){
    		bool sec=1;
    		for (int i=1,len=strlen(s);i<len-1;i++){
    			if (s[i-1]!=s[i+1]) continue;
    			if (getans(0,i-1)^getans(i+1,len-1)) continue;
    			printf("First
    %d
    ",i+1),sec=0;break;
    		}
    		if (sec) puts("Second");
    	}
    	return 0;
    }


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  • 原文地址:https://www.cnblogs.com/thythy/p/5493554.html
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