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Valid Parenthesis String in C++
Suppose we have an expression. The expression has some parentheses; we have to check the parentheses are balanced or not. The order of the parentheses are (), {} and []. Suppose there are two strings. “()[(){()}]” this is valid, but “{[}]” is invalid.
To solve this, we will follow these steps −
- Traverse through the expression until it has exhausted
- if the current character is opening bracket like (, { or [, then push into stack
- if the current character is closing bracket like ), } or ], then pop from stack, and
- check whether the popped bracket is corresponding starting bracket of the
- current character, then it is fine, otherwise, that is not balanced.
- After the string is exhausted, if there are some starting bracket left into the stack, then the string is not balanced.
Example(C++)
Let us see the following implementation to get better understanding −
#include <iostream>
#include <stack>
using namespace std;
bool isBalancedExp(string exp) {
stack<char> stk;
char x;
for (int i=0; i<exp.length(); i++) {
if (exp[i]=='('||exp[i]=='['||exp[i]=='{') {
stk.push(exp[i]);
continue;
}
if (stk.empty())
return false;
switch (exp[i]) {
case ')':
x = stk.top();
stk.pop();
if (x=='{' || x=='[')
return false;
break;
case '}':
x = stk.top();
stk.pop();
if (x=='(' || x=='[')
return false;
break;
case ']':
x = stk.top();
stk.pop();
if (x =='(' || x == '{')
return false;
break;
}
}
return (stk.empty());
}
int main() {
string expresion = "()[(){()}]";
if (isBalancedExp(expresion))
cout << "This is Balanced Expression";
else
cout << "This is Not Balanced Expression";
}Input
"()[(){()}]"Output
This is Balanced Expression
Updated on: 28-Apr-2020
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