640. Solve the Equation

1. Description

Given a string representing an equation, solve the equation.

2. Solution

Decode the string, put all 'x's into the left part of the equation, and put all numbers into the right part.

Judge whether there is a solution and return the solution.

3.Code

string solveEquation(string s) {
int a=0;
int b=0;
s=s+"+";
int n=s.size();
bool f=true;
string str;
bool add=true;
for(int i=0;i<n;i++){
if(s[i]=='+'||s[i]=='-'||s[i]=='='){
if(s[i-1]=='x'){
str = str.substr(0,str.size()-1);
int cnt;
if(str=="")
cnt=1;
else
cnt = atoi(str.c_str());
if(!add)
cnt=-cnt;
if(f)
a+=cnt;
else
a-=cnt;
}
else{
int cnt = atoi(str.c_str());
if(!add)
cnt=-cnt;
if(f)
b-=cnt;
else
b+=cnt;
}
if(s[i]=='=')
f=false;

if(s[i]=='-')
add=false;
else
add=true;
str="";
}
else
str+=s[i];
}

if(a==0&&b==0)
return "Infinite solutions";
else if(a==0)
return "No solution";
else
return "x="+to_string(b/a);
}