balanced-parenthesis

Author: SumeetHaryani

README.md

@@ -22,6 +22,8 @@ Collection of interview questions with Unit Tests. Problems includes Data Struct
   - [Implement Queue Using Stack](src/_DataStructures_/Stack/immitate-queue-using-stack)
   - [Baseball Game](src/_DataStructures_/Stack/baseball-game)
   - [Minimum Stack](src/_DataStructures_/Stack/min-stack)
+  - [Balanced Parenthesis](src/_DataStructures_/Stack/balanced-parenthesis)
+
 - [Queue](src/_DataStructures_/Queue)
   - [Weave](src/_DataStructures_/Queue/weave)
 

src/_DataStructures_/Stack/balanced-parenthesis/index.js

@@ -0,0 +1,43 @@
+/**
+ Given an expression string exp , write a program to examine whether the pairs and 
+ the orders of “{“,”}”,”(“,”)”,”[“,”]” are correct in expression.
+
+Example:
+Input: exp = “[()]{}{[()()]()}”
+Output: true
+
+Input: exp = “[(])”
+Output: false
+*/
+
+
+const Stack = require('../index');
+
+function checkBalancedParenthesis(expression) {
+    let s = new Stack();
+    for (let i = 0; i < expression.length; i++) {
+        const char = expression[i];
+        if (char === '{' || char === '(' || char === '[') {
+            //If current character is a starting bracket (‘(‘ or ‘{‘ or ‘[‘) then push it to stack
+            s.push(char);
+        } else {
+            if (s.isEmpty()) {
+                //when we have only right parenthesis or brackets in expresion
+                return false;
+            } else if (char === '}' && s.peek() !== '{' || char === ')' && s.peek() !== '(' || char === ']' && s.peek() !== '[') {
+                return false;
+            }
+            //If the current character is a closing bracket (‘)’ or ‘}’ or ‘]’) then pop it from stack
+            s.pop();
+        }
+    }
+    if (s.isEmpty()) {
+        //expression has balanced parenthesis
+        return true;
+    } else {
+        return false;
+    }
+}
+
+console.log(checkBalancedParenthesis("{()}[]")); //true
+console.log(checkBalancedParenthesis("{()}}")); //false

src/_DataStructures_/Stack/index.js

@@ -15,6 +15,9 @@ class Stack {
   peek() {
     return this.data[this.data.length - 1];
   }
+  isEmpty(){ //check if stack is empty
+    return this.data.length==0;
+  }
 }
 
 module.exports = Stack;