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/**
 * Valid Parentheses
 * @param {string} s
 * @return {boolean}
 */
const validParentheses = (s) => {
  if (s === null || !s.length) return true;

  const chars = s.split('');
  const stack = [];

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const twoSum = (numbers:number[], k: number): Boolean => {

    const rec:Record<number,number>= {};

    for(const n of numbers){
        rec[n] = n;
        if(rec.hasOwnProperty(k-n)) return true;
    }
 
    return false;

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const uniqueNumber = (arr:number[]):number => arr.reduce((x,y) => x^y);

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const couldBeMadeNonDecreasing = (arr:number[]):Boolean => {
    let decreasingPairs = 0
    for(let i in arr){
        if(arr[i] > arr[+i+1]){
            decreasingPairs++
        }
    }
    return decreasingPairs <= 1
}

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class MaxStack {

    private stack: number[] = new Array<number>();
    private maxStack: number[] = new Array<number>();
    private length: number = 0;

    public push(item: number): void {
        let previousMax = this.maxStack[this.length-1] || 0;
        this.maxStack[this.length] = item > previousMax ? item : previousMax;
        this.stack[this.length++] = item;

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// no recursion 
const waysToClimbStairs = (n:number):number => {
    const a:number[] = [1,1];
    if(n>1){
        for(let i = 2; i <= n ; i++){
            a[i] = a[i-1] + a[i-2];
        }
    };
    return a[a.length - 1];
}

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// without recursion 💪
const waysToClimbStairs = (n:number):number => {
    const a:number[] = [1,1];
    if(n>1){
        for(let i = 2; i <= n ; i++){
            a[i] = a[i-1] + a[i-2];
        }
    };
    return a[a.length - 1];
}

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const findPythagoreanTriplets = (arr:number[]):boolean => {

    if(arr.length<3) return false;

    const sorted = arr
    .map(v => v*v)
    .sort((a,b) => a-b);

    let [l,r,i] = [0, sorted.length -2, sorted.length -1];

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const getEditDistance = function(a: string, b: string):number{

  if(!a.length) return b.length; 
  if(!b.length) return a.length; 

  const matrix:number[][] = [];
  
  // fill first row and column 
  for(let i = 0; i <= b.length; i++){
    matrix[i] = [i];

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const word_search = (arr:string[][], word: string) : boolean => {

  if(word.length > arr.length) return false;

  let horizontal = '';
  let vertical:{ [key: string]: string } = {};

  for(let i=0; i<arr.length;i++){
    for(let j=0; j<arr[i].length;j++){
      horizontal+= arr[i][j];