Balanced parentheses problem added

TOC.md

@@ -75,6 +75,7 @@
 - [Maximum Product of Three Numbers](src/_Problems_/max-product-of-3-numbers)
 - [Next Greater for Every Element in an Array](src/_Problems_/next-greater-element)
 - [Compose Largest Number](src/_Problems_/compose-largest-number)
+- [Balanced Parentheses](src/_Problems_/balanced-parentheses)
 
 ### Searching
 

src/_Problems_/balanced-parentheses/balanced-parentheses.test.js

@@ -0,0 +1,28 @@
+const { balancedParantheses } = require('.');
+
+describe('Balanced parantheses in string', () => {
+  let str1, str2, str3, str4;
+
+  beforeEach(() => {
+    str1 = '(())';
+    str2 = '(((';
+    str3 = ')(';
+    str4 = '((()';
+  });
+
+  it('Should return TRUE for `(())`', () => {
+    expect(balancedParantheses(str1)).toBe(true);
+  });
+
+  it('Should return FALSE for `(((`', () => {
+    expect(balancedParantheses(str2)).toBe(false);
+  });
+
+  it('Should return TRUE for `)(`', () => {
+    expect(balancedParantheses(str3)).toBe(false);
+  });
+
+  it('Should return TRUE for `((()`', () => {
+    expect(balancedParantheses(str4)).toBe(false);
+  });
+});

src/_Problems_/balanced-parentheses/index.js

@@ -0,0 +1,27 @@
+/* 
+    Given a string containing characters and "(" , ")" determine if input string is valid if:
+    -  Open parantheses is closed by same number & type of parantheses.
+    Note that an empty string is also considered valid and any alphanumeric char can be inserted in between pratheses.
+
+    Example : 
+       ((())) is balanced.
+       ((() is not balanced.
+       )( is not balanced.
+    We will solve this problem using ES6 - Array Method reduce().
+ */
+
+function balancedParantheses(string) {
+  return !string.split('').reduce(function(prev, char) {
+    if (prev < 0) return prev;
+
+    if (char === '(') return ++prev;
+
+    if (char === ')') return --prev;
+
+    return prev;
+  }, 0);
+}
+
+module.exports = {
+  balancedParantheses,
+};