标签：
Description
Vanya is doing his maths homework. He has an expression of form , where x1, x2, ..., xn are digits from 1 to9, and sign
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 Input
3+5*7+8*4
303
2+3*5
25
3*4*5
60
Hint
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).
#include<iostream> #include<stdio.h> using namespace std; char exp[50005]; int t=3; long long cal(int left,int right) { long long now=0; long long ans=0; if(!left) { for(int i=1; i<t-1; i++) { if(exp[i]==‘+‘) { if(now) { ans+=now; now=0; } } else if(exp[i]==‘*‘) { now*=(exp[i+1]-‘0‘); i++; } else now=exp[i]-‘0‘; //cout<<now<<endl; } ans+=now; } else { long long tr=0; long long pos=0; for(int i=left+1; i<right; i++) { if(exp[i]==‘+‘) { if(pos) { tr+=pos; pos=0; } } else if(exp[i]==‘*‘) { pos*=(exp[i+1]-‘0‘); i++; } else pos=exp[i]-‘0‘; } tr+=pos; //cout<<tr<<endl; for(int i=1; i<t-1; i++) { if(exp[i]==‘+‘) { if(now) { ans+=now; now=0; } } else if(exp[i]==‘*‘) { if(i==left) { now*=tr; i=right-1; } else { now*=(exp[i+1]-‘0‘); i++; } } else now=exp[i]-‘0‘; } ans+=now; } return ans; } int main() { while(t) { exp[t++]=getchar(); if(exp[t-1]==‘\n‘) break; } exp[1]=‘1‘; exp[2]=‘*‘; exp[t-1]=‘*‘; exp[t++]=‘1‘; /*for(int i=1;i<t;i++) cout<<exp[i]<<" "; //cout<<cal(0,0);*/ long long ans=cal(0,0); for(int i=1; i<t-1; i++) { if(exp[i]==‘*‘) { for(int j=i+1; j<t-1; j++) { if(exp[i]==‘*‘) { ans=max(ans,cal(i,j)); } } } } printf("%I64d\n",ans); return 0; }
这道题就是要想明白括号为什么要必须放在两个乘号的之间。
然后因为乘号至多有15个，所以暴力一遍就行了。
标签：
原文地址：http://www.cnblogs.com/superxuezhazha/p/5428141.html
