TypeScript exercises

TypeScript/Problem1.ts

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+/*
+4. MEDIAN OF TWO SORTED ARAYS
+
+Given two sorted arrays nums1 and nums2 of size m and n respectively, return the median of the two sorted arrays.
+The overall run time complexity should be O(log (m+n)).
+Go to LeetCode and look for the problem #4, and read the examples for a better understanding.
+*/
+
+function findMedianSortedArrays(nums1: number[], nums2: number[]): number {
+  const totalLength = nums1.length + nums2.length;
+  const isEven = totalLength % 2 === 0;
+  const medianIndex = Math.floor(totalLength / 2);
+
+  let i = 0;
+  let j = 0;
+  let current = 0;
+  let previous = 0;
+
+  for (let k = 0; k <= medianIndex; k++) { // itera hasta alcanzar ell índice del elemento medio
+    previous = current; // guarda el valor actual en previous
+    if (i < nums1.length && (j >= nums2.length || nums1[i] < nums2[j])) { // compara los elementos de los arrays y selecciona el menor
+      current = nums1[i]; // asigna el index de nums1 a current
+      i++; // y avanza el index i
+    } else {
+      current = nums2[j]; // asigna el valor de nums2 a current
+      j++; // y avanza index j
+    }
+  }
+
+  return isEven ? (previous + current) / 2 : current; // si isEven resulta true, devuelve la division
+                                                      // entre 2 de la suma de previous y current.
+                                                      // Si isEven es false, devuelve current.
+};

TypeScript/Problem2.ts

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+/*
+146. LRU CACHE
+Design a data structure that follows the constraints of a Least Recently Used (LRU) cache.
+Go to LeetCodde and look for the problem #146, and read the instructions to understand this better.
+*/
+
+class LRUCache {
+  private capacity: number;
+  private cache: Map<number, number>;
+
+  constructor(capacity: number) {
+    if (capacity < 1 || capacity > 3000) {
+      throw new Error("Capacity must be between 1 and 3k");
+    }
+    this.capacity = capacity;
+    this.cache = new Map();    
+  }
+
+  get(key: number): number {
+    if (!this.cache.has(key)) {//si no existe, -1
+      return -1;
+    }
+
+    //En caso de sí tenerla, la mueve al final (más reciente)
+    const temp = this.cache.get(key)!;
+    this.cache.delete(key);
+    this.cache.set(key, temp);
+    return temp; 
+  }
+
+  put(key: number, value: number): void {
+    if (key < 0 || key > 10000) {
+      throw new Error("Key must be between 0 and 10k");
+    }
+
+    if (value < 0 || value > 100000) {
+      throw new Error("Value must be between 0 and 100k");
+    }
+
+    if (this.cache.has(key)) { //si ya existe, lo elimina
+      this.cache.delete(key);
+    } else if (this.cache.size == this.capacity) { //si no existía y no hay más memoria
+      //elimina la clave mas vieja
+      const [oldestKey] = this.cache.keys();
+      this.cache.delete(oldestKey);
+    }
+    this.cache.set(key, value); //vuelve a insertar la key preexistente para actualizarla al lugar mas reciente
+  }
+}
+
+/**
+* Your LRUCache object will be instantiated and called as such:
+* var obj = new LRUCache(capacity)
+* var param_1 = obj.get(key)
+* obj.put(key,value)
+*/

TypeScript/Problem3.ts

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+/*
+3. LONGEST SUBSTRING WITHOUT REPEATING CHARACTERS
+Given a string s, find the length of the longest substring without duplicate characters.
+Go to LeetCode and look for the problem #3, and read the instructions for a better understanding.
+*/
+
+function lengthOfLongestSubstring(s: string): number {
+  let characterIndexList: Map<string, number> = new Map(); //aqui se almacenan los strings con su valor
+  let maxLength: number = 0; //maxima longitud histórica
+  let left: number = 0; //limite izquierdo indica a partir de dónde no hay caracteres repetidos
+
+  for (let index = 0; index < s.length; index++) {
+    if (characterIndexList.has(s[index])) { //si el caracter ya existe en map
+      left = Math.max(left, characterIndexList.get(s[index])!+1); //mueve left delante de la posicion repetida
+    }
+
+    characterIndexList.set(s[index], index); //agrega el caracter al map. En caso de ya existir, actualiza su valor
+    maxLength = Math.max(maxLength, index - left + 1); //evalua qué valor es mayor: la longitud maxima registrada o la actual respecto a left
+  }
+
+  return maxLength;
+};

TypeScript/Problem4.ts

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+/*
+10. REGULAR EXPRESSION MATCHING
+Given an input string s and a pattern p, implement regular expression matching with support for '.' and '*' where:
+'.' Matches any single character.​​​​
+'*' Matches zero or more of the preceding element.
+The matching should cover the entire input string (not partial).
+
+Go to LeetCode and look for the problem #10. Read the examples for a better understanding.
+*/
+
+function isMatch(s: string, p: string): boolean {
+  const dp: boolean[][] = Array(s.length + 1).fill(null).map(() => Array(p.length + 1).fill(false));  //crea matriz en false
+  dp[0][0] = true; //true porque las cadenas al inicio coinciden al estar vacias
+
+  for (let j = 2; j <= p.length; j += 2) { //maneja patrones como "a*" o ".*" al inicio
+    if (p[j - 1] === '*') {
+      dp[0][j] = dp[0][j - 2];
+    }
+  }
+
+  //compara cada caracter de la cadena con el patron
+  for (let i = 1; i <= s.length; i++) {
+    for (let j = 1; j <= p.length; j++) {
+      if (p[j - 1] === s[i - 1] || p[j - 1] === '.') { //si coinciden exactamente o es "."
+        dp[i][j] = dp[i - 1][j - 1];
+      } else if (p[j - 1] === '*') { //en caso de encontrar "*"
+        dp[i][j] = dp[i][j - 2]; //opcion 1: no se usa el caracter previo
+
+        if (p[j - 2] === s[i - 1] || p[j - 2] === '.') {
+          dp[i][j] = dp[i][j] || dp[i - 1][j]; //opcion 2: se usa el carácter previo si coincide con el actual de s
+        }
+      }
+    }
+  }
+
+  return dp[s.length][p.length]; //se comparan las cadenas
+}