CF552E 字符串 表达式求值

http://codeforces.com/contest/552/problem/E

E. Vanya and Brackets
time limit per test

1 second

memory limit per test

256 megabytes

input

standard input

output

standard output

Vanya is doing his maths homework. He has an expression of form CF552E 字符串 表达式求值,
where x1, x2, ..., xn are
digits from 1 to 9, and
sign CF552E 字符串 表达式求值 represents
either a plus '+' or the multiplication sign '*'.
Vanya needs to add one pair of brackets in this expression so that to maximize the value of the resulting expression.

Input

The first line contains expression s (1 ≤ |s| ≤ 5001, |s| is
odd), its odd positions only contain digits from 1 to 9,
and even positions only contain signs  +  and  * .

The number of signs  *  doesn't exceed 15.

Output

In the first line print the maximum possible value of an expression.

Sample test(s)
input
3+5*7+8*4
output
303
input
2+3*5
output
25
input
3*4*5
output
60
Note

Note to the first sample test. 3 + 5 * (7 + 8) * 4 = 303.

Note to the second sample test. (2 + 3) * 5 = 25.

Note to the third sample test. (3 * 4) * 5 = 60 (also many other variants are valid, for instance, (3) * 4 * 5 = 60).

/**
CF552E 字符串 表达式求值
题目大意:给定一个字符串仅仅是做1~9之间的加法和乘法,如今在表达式中加上一对括号。问怎样加才干使表达式的值最大
解题思路:左括号必须在一个*的后面,右括号必须在一个*的前面,假设不是这样一定不是最优。 有了这个结论,分成三部分算一下就能够了
*/
#include <string.h>
#include <iostream>
#include <algorithm>
#include <stdio.h>
using namespace std;
typedef long long LL;
char s[5005];
int n,a[105];
LL get(int l,int r)
{
LL ans=0,tmp=1;
for(int i=l;i<=r;i++)
{
if(isdigit(s[i]))
{
tmp*=s[i]-'0';
}
if(s[i]=='+')
{
ans+=tmp;
tmp=1;
}
}
ans+=tmp;
tmp=1;
LL sum=0;
for(int i=0;i<n;i++)
{
if(i==l)
{
tmp*=ans;
i=r;
}
else
{
if(isdigit(s[i]))
{
tmp*=s[i]-'0';
}
if(s[i]=='+')
{
sum+=tmp;
tmp=1;
}
}
}
sum+=tmp,tmp=1;
// printf(">>>%d %d %d %d\n",l,r,ans,sum);
return sum;
}
int main()
{
scanf("%s",s);
n=strlen(s);
int k=0;
a[k++]=0;
for(int i=0;i<n;i++)
{
if(s[i]=='*')
{
a[k++]=i-1;
a[k++]=i+1;
}
}
if(a[k-1]!=n-1)
a[k++]=n-1;
LL maxx=0;
for(int i=0;i<k;i++)
{
for(int j=i;j<k;j++)
{
LL t=get(a[i],a[j]);
maxx=max(maxx,t);
}
}
printf("%lld\n",maxx);
return 0;
}
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