## String to Integer (AtoI – ASCII to Integer) – Recursive Solution

Objective: Write a recursive function to implement atoi, which converts string to an integer. Rules for converting string to an integer. If the string is null or empty, Integer will be 0. The first character of the string may represent the sign of the integer. ‘+’ or ‘-‘ Discard the white spaces if necessary. If … Read more String to Integer (AtoI – ASCII to Integer) – Recursive Solution

## Longest contiguous character in a given String – O(N) Solution

Objective: Given an input string, write an algorithm to find the longest contiguous character or in other words, find a maximum consecutive character in the string. Example: Input: “aaabbccccddbbaaa” Output: c, count = 4 Input: “bbbbb” Output: b, count=5 Approach: Naive Approach:  Naive Approach: Use  two nested loops The outer loop to fix it on … Read more Longest contiguous character in a given String – O(N) Solution

## Convert Postfix to Infix Expression

Objective: Given a Postfix expression, write an algorithm to convert it into Infix expression. Example: Input: Postfix expression:  A B +  Output: Infix expression- (A + B) Input: Postfix expression:  ABC/-AK/L-* Output: Infix expression: ((A-(B/C))*((A/K)-L)) Approach: Use Stack Algorithm: Iterate the given expression from left to right, one character at a time If a character … Read more Convert Postfix to Infix Expression

## String to Integer (AtoI – ASCII to Integer)

Objective: Implement atoi, which converts string to an integer. Rules for converting string to an integer. If the string is null or empty, Integer will be 0. The first character of string may represent the sign of the integer. ‘+’ or ‘-‘ Discard the white spaces if necessary. If any point, conversion of the string … Read more String to Integer (AtoI – ASCII to Integer)

## Longest substring with at most two unique characters

Objective: Given a string, write an algorithm to find the longest substring with at most two characters. Example: Input: aabbccddc Output: ccddc, length: 5 Input: aabacbeeeebeaabb Output: beeeebe, length 7 Input: aaaaaa Output: Only one unique character is present in the input string Approach: Brute Force Identify all the substrings of the given input string … Read more Longest substring with at most two unique characters

## Convert Prefix to Infix Expression

Objective: Given a Prefix expression, write an algorithm to convert it into Infix expression. Example: Input: Prefix expression: + A B Output: Infix expression- (A + B) Input: Prefix expression: *-A/BC-/AKL Output: Infix expression: ((A-(B/C))*((A/K)-L)) Approach: Use Stacks Algorithm: Iterate the given expression from right to left (in reverse order), one character at a time … Read more Convert Prefix to Infix Expression

## Convert Infix to Prefix Expression

Objective: Given an Infix expression, write an algorithm to convert it into Prefix expression. Example: Input: Infix expression – A + B Output: Prefix expression- +AB Input: Infix expression – A+B*(C^D-E) Output: Prefix expression- +A*B-^CDE Approach: Use Stack Operator stack: This stack will be used to keep operations (+, -, *, /, ^) Order of … Read more Convert Infix to Prefix Expression

## Find duplicates Characters in the given String

Objective: Given a string, write an algorithm to find all the duplicate characters in the string and print its count. Example: Input String: tutorial horizon Output: Duplicate Characters: r – 2 t – 2 i – 2 o – 3 Approach: Hash Map Maintain a Hash Map with Character as key and count as value. … Read more Find duplicates Characters in the given String

## Convert Infix to Postfix Expression

Objective: Given an Infix expression, write an algorithm to convert it into Postfix expression. Example: Input: Infix expression – A + B Output: Postfix expression- AB+ Input: Infix expression – A+B*(C^D-E) Output: Postfix expression- ABCD^E-*+ Approach: Use Stacks Operator stack: This stack will be used to keep operations (+, -, *, /, ^) Order of … Read more Convert Infix to Postfix Expression

## Evaluation of Infix expressions

Infix notation is commonly used in arithmetic formula or statements, the operators are written in-between their operands. Let’s assume the below Operands are real numbers. Permitted operators: +,-, *, /, ^(exponentiation) Blanks are permitted in expression. Parenthesis are permitted Example: A * ( B + C ) / D 2 * (5 + 3) / … Read more Evaluation of Infix expressions

## Infix, Postfix and Prefix Notations/Expressions

Infix, Postfix and Prefix notations are most common ways of writing expressions. Infix notation: Example: (A+B) Infix notation is commonly used in arithmetic formula or statements, the operators are written in-between their operands. An expression such as A * ( B + C ) / D is solved as: First add B and C. Multiply … Read more Infix, Postfix and Prefix Notations/Expressions

## Valid Multiple Parentheses

Objective: Given a string containing just the characters ‘(‘, ‘)’, ‘{‘, ‘}’, ‘[‘ and ‘]’, determine if the input string is valid. Example: ()()([]({}))[] valid: true ()({]) valid: false []{}() valid: true [(}{)] valid: false Earlier we had seen problem Valid Parentheses, where only one type of parentheses was present in the input string, in this problem we can have multiple types … Read more Valid Multiple Parentheses

## Valid Brackets – Part 2 | Stack Method

Objective: Given a string containing just the characters ( , ) determine if the input string is valid. Example: ()()(()(()))() valid: true )()()( valid: false ()()) valid: false Approach: Earlier we discussed the solution which keeps the count of open and closed parentheses. In this solution we will solve this problem using stack. Using Stack: Initialize a … Read more Valid Brackets – Part 2 | Stack Method

## Given two strings validate the output string

Objective: Given two input strings and one output strings, validate if output string contains all the characters from both the input strings. Example: Input1 = “boy”, Input2 = “girl”, output = “gboilry” Result = True Input1 = “tutorial”, Input2 = “horizon”, output = “tuhotoririzoialn” Result = True Input1 = “boy”, Input2 = “girl”, output = … Read more Given two strings validate the output string

## Generate all the strings of length n from 0 to k-1.

Objective: Given two numbers, n and k (k>=n), write an algorithm to generate all the strings of length n drawn from 0 – k-1. Example: k = 2, n = 2Output:  0 0      0 1         1 0         1 1 k = 3, n = 2 Output: 0 0         1 0        2 0        0 1         1 … Read more Generate all the strings of length n from 0 to k-1.