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Commit f6d18ed

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Merge pull request #33 from SumeetHaryani/master
Added postfix expression evaluation problem
2 parents 17eebb1 + c1508a8 commit f6d18ed

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4 files changed

+78
-6
lines changed

4 files changed

+78
-6
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‎README.md

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@@ -26,7 +26,10 @@ Collection of interview questions with Unit Tests. Problems includes Data Struct
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- [Baseball Game](src/_DataStructures_/Stack/baseball-game)
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- [Minimum Stack](src/_DataStructures_/Stack/min-stack)
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- [Balanced Parenthesis](src/_DataStructures_/Stack/balanced-parenthesis)
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- [Postfix Expression Evaluation](src/_DataStructures_/Stack/postfix-expression-evaluation)
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- [Remove Consecutive Repeated Digits](src/_DataStructures_/Stack/remove-consecutive-repeated-digits)
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- [Implement 2 Stacks using Single Array](src/_DataStructures_/Stack/2-stacks-using1-array)
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- [Queue](src/_DataStructures_/Queue)
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- [Weave](src/_DataStructures_/Queue/weave)

‎src/_Classics_/fibonacci/index.js

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@@ -1,9 +1,11 @@
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//The Fibonacci sequence: 0, 1, 1, 2, 3, 5, 8, 13, 21
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// the algorithm has time complexity of O(n^2), very bad!
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function fibonacci(position) {
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// if position is 1 or 2, the number in fibonacci sequence will be 1
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if (position <3) {
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return 1;
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if (position <=1) {
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return position;
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}
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// else the element in fibonacci sequence will be the sum of
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// element at position(p) (p -1) and (p - 2)
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return fibonacci(position - 2) + fibonacci(position - 1);
@@ -24,8 +26,8 @@ function fibonacciMemoized(index, cache) {
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if (cache[index]) {
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return cache[index];
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} else {
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if (index <3) {
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return 1;
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if (index <=1) {
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return index;
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} else {
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cache[index] =
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fibonacciMemoized(index - 1, cache) +
@@ -41,7 +43,9 @@ function fibonacciMemoized(index, cache) {
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function fibonacciTabular(n) {
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const table = [0, 1];
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if (n <= 1) {
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return n;
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}
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for (let i = 2; i <= n; i += 1) {
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table[i] = table[i - 1] + table[i - 2];
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}
@@ -54,4 +58,4 @@ function fibonacciTabular(n) {
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// console.log(`Fib normal - ${fibonacci(number)}`);
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// console.log('--');
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// console.log(`Fib memo - ${fibonacciMemoized(number)}`);
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// console.log(`Fib table - ${fibonacciTabular(number)}`);
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// console.log(`Fib table - ${fibonacciTabular(number)}`);
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/**
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* Evaluation of Postfix Expression
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* Input:456*+
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* Output:34
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*/
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const Stack = require('../index');
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function evaluatePostfixExpression(expression) {
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let s = new Stack();
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for (let i = 0; i < expression.length; i++) {
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const char = expression[i];
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if (!isNaN(char)) {
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//if number push the char onto stack
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s.push(Number(char));
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} else {
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// if char is an operator then pop two elements from stack, evaluate them accordingly based on operator.
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//push the result to stack
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let val1 = s.pop();
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let val2 = s.pop()
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switch (char) {
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case '+':
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s.push(val2 + val1);
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break;
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case '-':
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s.push(val2 - val1);
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break;
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case '*':
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s.push(val2 * val1);
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break;
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case '/':
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s.push(val2 / val1);
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break;
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}
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}
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}
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//pop the value of postfix expression
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return s.pop();
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}
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/**
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* Given an integer N, remove consecutive repeated digits from it.
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* Input:133445
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* Output:1345
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*/
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const Stack = require('../index');
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function removeConsecutiveDigits(no) {
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let s = new Stack();
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let newNo = "";
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//initally push first digit into stack
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newNo += no[0];
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s.push(no[0]);
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for (let i = 1; i < no.length; i++) {
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const digit = no[i];
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//if stack top and incoming digit is same ignore it else append to newNo.
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if (s.peek() !== digit) {
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newNo += digit;
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s.push(digit);
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}
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}
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return newNo
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}

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