#define is unsafe——I
I. #define is unsafe
Have you used #define in C/C++ code like the code below?
#include <stdio.h>
#define MAX(a , b) ((a) > (b) ? (a) : (b))
int main()
{
printf("%d\n" , MAX(2 + 3 , 4));
return 0;
}
Run the code and get an output: 5, right?
You may think it is equal to this code:
#include <stdio.h>
int max(a , b) { return ((a) > (b) ? (a) : (b)); }
int main()
{
printf("%d\n" , max(2 + 3 , 4));
return 0;
}
But they aren't.Though they do produce the same anwser , they work in two different ways.
The first code, just replace the MAX(2 + 3 , 4) with ((2 + 3) > (4) ? (2 + 3) : 4), which calculates (2 + 3) twice.
While the second calculates (2 + 3) first, and send the value (5 , 4) to function max(a , b) , which calculates (2 + 3) only once.
What about MAX( MAX(1+2,2) , 3 ) ?
Remember "replace".
First replace: MAX( (1 + 2) > 2 ? (1 + 2) : 2 , 3)
Second replace: ( ( ( 1 + 2 ) > 2 ? ( 1 + 2 ) : 2 ) > 3 ? ( ( 1 + 2 ) > 2 ? ( 1 + 2 ) : 2 ) : 3).
The code may calculate the same expression many times like ( 1 + 2 ) above.
So #define isn't good.In this problem,I'll give you some strings, tell me the result and how many additions(加法) are computed.
#include <stdio.h>
#define MAX(a , b) ((a) > (b) ? (a) : (b))
int main()
{
printf("%d\n" , MAX(2 + 3 , 4));
return 0;
}
Run the code and get an output: 5, right?
You may think it is equal to this code:
#include <stdio.h>
int max(a , b) { return ((a) > (b) ? (a) : (b)); }
int main()
{
printf("%d\n" , max(2 + 3 , 4));
return 0;
}
But they aren't.Though they do produce the same anwser , they work in two different ways.
The first code, just replace the MAX(2 + 3 , 4) with ((2 + 3) > (4) ? (2 + 3) : 4), which calculates (2 + 3) twice.
While the second calculates (2 + 3) first, and send the value (5 , 4) to function max(a , b) , which calculates (2 + 3) only once.
What about MAX( MAX(1+2,2) , 3 ) ?
Remember "replace".
First replace: MAX( (1 + 2) > 2 ? (1 + 2) : 2 , 3)
Second replace: ( ( ( 1 + 2 ) > 2 ? ( 1 + 2 ) : 2 ) > 3 ? ( ( 1 + 2 ) > 2 ? ( 1 + 2 ) : 2 ) : 3).
The code may calculate the same expression many times like ( 1 + 2 ) above.
So #define isn't good.In this problem,I'll give you some strings, tell me the result and how many additions(加法) are computed.
Input
The first line is an integer T(T<=40) indicating case number.
The next T lines each has a string(no longer than 1000), with MAX(a,b), digits, '+' only(Yes, there're no other characters).
In MAX(a,b), a and b may be a string with MAX(c,d), digits, '+'.See the sample and things will be clearer.
The next T lines each has a string(no longer than 1000), with MAX(a,b), digits, '+' only(Yes, there're no other characters).
In MAX(a,b), a and b may be a string with MAX(c,d), digits, '+'.See the sample and things will be clearer.
Output
For each case, output two integers in a line separated by a single space.Integers in output won't exceed 1000000.
Sample Input
6 MAX(1,0) 1+MAX(1,0) MAX(2+1,3) MAX(4,2+2) MAX(1+1,2)+MAX(2,3) MAX(MAX(1+2,3),MAX(4+5+6,MAX(7+8,9)))+MAX(10,MAX(MAX(11,12),13))
Sample Output
1 0 2 1 3 1 4 2 5 2 28 14
题目大意:给定一个只含有MAX和+操作的式子,求加法运行了多少次,
分析:
MAX(A,B)其中A中加a次,B中加b次若A>B,则加a*2+b次,否则a+b*2次。
#include <cstdio> #include <iostream> #include <cstring> using namespace std; struct state{ state(int a,int b){s=a,k=b;} int s,k; //s为和,k为次数 }; state find(string str){ int in=0,len=str.length(),num=0;//当前位置,字符串长度,和 if(str[in]>='0'&&str[in]<='9'){ //第一个字母是整数,读取这个数 while(in<len&&str[in]>='0'&&str[in]<='9')num=num*10+str[in++]-'0'; if(in>=len)return state(num,0);//如果只剩一个数,直接返回 else{ state st=find(str.substr(in+1)); return state(num+st.s,st.k+1); } }else if(str[in]=='M'){ in+=4; int cnt=1,mid=0; while(cnt>0){ //匹配MAX()右括号的位置,并找出对应这个MAX的逗号的位置 if(str[in]=='(')cnt++; else if(str[in]==')')cnt--; if(str[in]==','&&cnt==1)mid=in; in++; } state le=find(str.substr(4,mid-4)); //求MAX(A,B)中的A state ri=find(str.substr(mid+1,in-mid-2)); //求MAX(A,B)中的B int p1,p2; if(le.s>ri.s){ p1=le.s; p2=le.k*2+ri.k; }else{ p1=ri.s; p2=le.k+ri.k*2; } if(in>=len-1){ //已经到达末端 return state(p1,p2); }else{ //MAX(A,B) + C的形式,求C state st=find(str.substr(in+1)); //处理加号后面的部分 return state(p1+st.s,st.k+p2+1); } } } int main(){ int cas; char str[1005]; cin>>cas; while(cas--){ cin>>str; state rs=find(str); cout<<rs.s<<" "<<rs.k<<endl; } return 0; }