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C++ Program to Check for balanced paranthesis by using Stacks
Here we will discuss how to check the balanced brackets using stacks. We not only check the opening and closing brackets but also check the ordering of brackets. For an example we can say that the expression "[{} () {()}]" it is correct, but "{[}]" it is not correct.
Input: Some expression with brackets "{()}[]"
Output: They are balancedAlgorithm
Step 1: Define a stack to hold brackets
Step 2: Traverse the expression from left to right
Step 2.1: If the character is opening bracket (, or { or [, then push it into stack
Step 2.2: If the character is closing bracket ), } or ] Then pop from stack, and if the popped character is matched with the starting bracket then it is ok. otherwise they are not balanced.
Step 3: After traversal if the starting bracket is present in the stack then it is not balanced.Example Code
#include<iostream>
#include<stack>
using namespace std;
bool isBalanced(string expr) {
stack<char> s;
char ch;
for (int i=0; i<expr.length(); i++) { //for each character in the expression, check conditions
if (expr[i]=='('||expr[i]=='['||expr[i]=='{') { //when it is opening bracket, push into stack
s.push(expr[i]);
continue;
}
if (s.empty()) //stack cannot be empty as it is not opening bracket, there must be closing bracket
return false;
switch (expr[i]) {
case ')': //for closing parenthesis, pop it and check for braces and square brackets
ch = s.top();
s.pop();
if (ch=='{' || ch=='[')
return false;
break;
case '}': //for closing braces, pop it and check for parenthesis and square brackets
ch = s.top();
s.pop();
if (ch=='(' || ch=='[')
return false;
break;
case ']': //for closing square bracket, pop it and check for braces and parenthesis
ch = s.top();
s.pop();
if (ch =='(' || ch == '{')
return false;
break;
}
}
return (s.empty()); //when stack is empty, return true
}
main() {
string expr = "[{}(){()}]";
if (isBalanced(expr))
cout << "Balanced";
else
cout << "Not Balanced";
}Output
Balanced
Updated on: 30-Jul-2019
8K+ Views
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