题意：给定一个长度为 n 的小写字母串。可以将出现次数大于等于2的字母全部变成另一个小写字母，问最后能否将该小写字母串的所有字母变成同一个字母
n<=1e5
思路：
1 #include<cstdio> 2 #include<cstring> 3 #include<string> 4 #include<cmath> 5 #include<iostream> 6 #include<algorithm> 7 #include<map> 8 #include<set> 9 #include<queue> 10 #include<vector> 11 using namespace std; 12 typedef long long ll; 13 typedef unsigned int uint; 14 typedef unsigned long long ull; 15 typedef pair<int,int> PII; 16 typedef vector<int> VI; 17 #define fi first 18 #define se second 19 #define MP make_pair 20 #define N 1100000 21 #define MOD 1000000007 22 #define eps 1e-8 23 #define pi acos(-1) 24 #define oo 110000000000000 25 26 char a[N]; 27 int b[N],c[N]; 28 29 30 int read() 31 { 32 int v=0,f=1; 33 char c=getchar(); 34 while(c<48||57<c) {if(c=='-') f=-1; c=getchar();} 35 while(48<=c&&c<=57) v=(v<<3)+v+v+c-48,c=getchar(); 36 return v*f; 37 } 38 39 40 void swap(int &x,int &y) 41 { 42 int t=x;x=y;y=t; 43 } 44 45 46 47 int main() 48 { 49 //freopen("1.in","r",stdin); 50 //freopen("1.out","w",stdout); 51 int n; 52 scanf("%d",&n); 53 scanf("%s",a+1); 54 for(int i=1;i<=n;i++) b[a[i]-'a'+1]++; 55 if(n==1) printf("Yes "); 56 else 57 { 58 int flag=0; 59 for(int i=1;i<=26;i++) 60 if(b[i]>=2) flag=1; 61 if(flag) printf("Yes "); 62 else printf("No "); 63 } 64 return 0; 65 }