LA 6979 Known Notation 构造+贪心铜牌题-白红宇

LA 6979 Known Notation 构造+贪心铜牌题

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发布时间：2019-06-13

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6979 Known Notation

Do you know reverse Polish notation (RPN)? It is a known notation in the area of mathematics and

computer science. It is also known as postfix notation since every operator in an expression follows all

of its operands. Bob is a student in Marjar University. He is learning RPN recent days.

To clarify the syntax of RPN for those who haven’t learnt it before, we will offer some examples

here. For instance, to add 3 and 4, one would write “3 4 +” rather than “3 + 4”. If there are multiple

operations, the operator is given immediately after its second operand. The arithmetic expression

written “3 - 4 + 5” in conventional notation would be written “3 4 - 5 +” in RPN: 4 is first subtracted

from 3, and then 5 added to it. Another infix expression “5 + ((1 + 2) × 4) - 3” can be written down

like this in RPN: “5 1 2 + 4 × + 3 -”. An advantage of RPN is that it obviates the need for parentheses

that are required by infix.

In this problem, we will use the asterisk “*” as the only operator and digits from “1” to “9” (without

“0”) as components of operands.

You are given an expression in reverse Polish notation. Unfortunately, all space characters are

missing. That means the expression are concatenated into several long numeric sequence which are

separated by asterisks. So you cannot distinguish the numbers from the given string.

You task is to check whether the given string can represent a valid RPN expression. If the given

string cannot represent any valid RPN, please find out the minimal number of operations to make it

valid. There are two types of operation to adjust the given string:

1. Insert. You can insert a non-zero digit or an asterisk anywhere. For example, if you insert a “1”

at the beginning of “2*3*4”, the string becomes “12*3*4”.

2. Swap. You can swap any two characters in the string. For example, if you swap the last two

characters of “12*3*4”, the string becomes “12*34*”.

The strings “2*3*4” and “12*3*4” cannot represent any valid RPN, but the string “12*34*” can

represent a valid RPN which is “1 2 * 34 *”.

Input

There are multiple test cases. The first line of input contains an integer T indicating the number of

test cases. For each test case:

There is a non-empty string consists of asterisks and non-zero digits. The length of the string will

not exceed 1000.

Output

For each test case, output the minimal number of operations to make the given string able to represent

a valid RPN.

Sample Input

1*1

11*234**

*ACM-ICPC Live Archive: 6979 – Known Notation 2/2

Sample Output

给出一个字符串，有两种操作： 1.插入一个数字 2.交换两个字符问最少多少步可以把该字符串变为一个后缀表达式（操作符只有*）

#include 
     
      #include 
      
       #include 
       
        #include 
        
         #include 
         
          #include 
          
           #include 
           #include 
            
             #include 
             
              #include 
              
               #include 
               
                #include 
                
                 #include 
                 
                  #define MM(a,b) memset(a,b,sizeof(a));#define inf 0x3f3f3f3fusing namespace std;typedef long long ll;typedef unsigned long long ull;#define CT continue#define SC scanfchar s[1005];int main(){ int cas;SC("%d",&cas); while(cas--){ SC("%s",s); int len=strlen(s),num=0,ln=0,star=0,ans=0; for(int i=0;s[i]!='\0';i++) if(s[i]=='*') star++; else num++; if(num
                  
                   ='0'&&s[i]<='9') ln++; else{ if(ln>=2) ln-=1; else { ans++; for(int j=len-1;j>=0;j--) if(s[j]!='*'){ swap(s[j],s[i]);ln++;break; } } } } printf("%d\n",ans); } return 0;}