Java(javac 1.8) 解法, 执行用时: 121ms, 内存消耗: 17272K, 提交时间: 2020-12-25 20:39:19

import java.util.Scanner;
public class Main {
	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		String zifu = in.next();
		long a[] = new long[4];
		for(int i =0;i<zifu.length();i++)
		{
			if(zifu.charAt(i) == 'C')
			{
				a[1] += a[0];
				a[0]++;
			}
			else if (zifu.charAt(i) == 'S') {
				a[2] += a[1];
			}
			else if (zifu.charAt(i) == 'U') {
				a[3] +=a[2];
			}
		}
		a[0] %= 1000000007;
		a[1] %= 1000000007;
		a[2] %= 1000000007;
		a[3] %= 1000000007;
		System.out.println(a[3]);
		in.close();
	}
}

C++(clang++11) 解法, 执行用时: 7ms, 内存消耗: 516K, 提交时间: 2020-12-20 16:56:00

#include <bits/stdc++.h>
using namespace std;

int main()
{string s;long long c,u,num; cin >> s; c = u = num = 0; for( int i = 0 ; i<s.length() ; i++ ) { if( s[i]=='U' ) u++; }
 for( int i = 0 ; i<s.length() ; i++ ) {if( s[i]=='C' ) c++; else if( s[i]=='U' ) u--; else if( s[i]=='S' )
 { num+=c*(c-1)/2*u; }
 } cout << num%1000000007 ;
}