solved on 16-02-26

js-built-ins/problems/easy/countOccurrences.js

@@ -20,7 +20,17 @@
 
 
 function countOccurrences(arr) {
-  // Your code here
+  let n=arr.length;
+  let freq={};
+  for(let i=0; i<n; i++){
+      if (freq[arr[i]]==undefined){
+          freq[arr[i]]=1;
+      }
+      else{
+          freq[arr[i]]++;
+      }
+  }
+  return freq;
 }
 
 module.exports = countOccurrences;

js-built-ins/problems/easy/countVowels.js

@@ -26,7 +26,13 @@
 */
 
 function countVowels(str) {
-  // Your code here
+  let s=str;
+  let cnt=0;
+
+  for (let ch of s.toLowerCase()){
+    if ("aeiou".includes(ch)) cnt++;
+  }
+  return cnt;
 }
 
 module.exports = { countVowels };

js-built-ins/problems/easy/fibonacci.js

@@ -39,12 +39,28 @@
 
 // Iterative Fibonacci function
 function fibonacci(n) {
-  // Your code here
+  n-=2;
+
+  let prev=0;
+  let curr=1;
+  let arr=[0,1];
+
+  while(n){
+      summ=prev+curr;
+      prev=curr;
+      curr=summ;
+      arr.push(summ);
+      n--;
+  }
+  return arr;
 }
 
 // Recursive Fibonacci function
 function fibonacciRecursive(n) {
-  // Your code here
+  if(n==0) return 0;
+  if(n==1) return 1
+
+  return fibonacciRecursive(n-1)+fibonacciRecursive(n-2);
 }
 
 module.exports = { fibonacci, fibonacciRecursive };

js-built-ins/problems/easy/reverseString.js

@@ -19,7 +19,8 @@
 */
 
 function reverseString(str) {
-  // Your code here
+  let reversed=str.split("").reverse().join("");
+  return reversed;
 }
 
 module.exports = reverseString;

js-built-ins/problems/hard/uniqueElements.js

@@ -14,12 +14,26 @@
   - Input: []
   - Output: []
 
+  just to test
+
   Once you've implemented the logic, test your code by running
   - `npm run test-unique`
 */
 
 function getUniqueElements(arr) {
-  // Your code here
+  let seen=new Set();
+  let narr=[];
+
+  for(let num of arr){
+
+
+    if(!seen.has(num)){
+      narr.push(num);
+      seen.add(num);
+    }
+
+  }
+  return narr;
 }
 
-module.exports = getUniqueElements;
+module.exports = getUniqueElements;

js-built-ins/problems/hard/wordCompression.js

@@ -23,7 +23,22 @@
 
 
 function compressWords(arr) {
-  // Your code here
+  let n=arr.length;
+  let narr=[];
+  let cnt=0;
+  for(let i=0; i<n; i++){
+    cnt++;
+    if(arr[i]!==arr[i+1]){
+      if(cnt>1){
+        narr.push(arr[i]+cnt);
+      }
+      else{
+        narr.push(arr[i]);
+      }
+      cnt=0;
+    }
+  }
+  return narr;
 }
 
 

js-built-ins/problems/medium/findDuplicates.js

@@ -23,5 +23,4 @@ function findDuplicates(arr) {
   return arr.filter((ele, index) => arr.indexOf(ele) !== index);
 }
 
-module.exports = findDuplicates;
-
+module.exports = findDuplicates;

js-built-ins/problems/medium/isPerfectNumber.js

@@ -26,7 +26,27 @@
 */
 
 function isPerfectNumber(num) {
-  // Your code here
+  if (num <= 1) return false;
+
+  let summ = 0;
+
+  for (let i = 1; i * i <= num; i++) {
+
+    if (num % i === 0) {
+
+      if (i !== num) {
+        summ += i;
+      }
+
+      let other = num / i;
+
+      if (other !== i && other !== num) {
+        summ += other;
+      }
+    }
+  }
+
+  return summ === num;
 }
 
 module.exports = { isPerfectNumber };

js-built-ins/problems/medium/non-repeat.js

@@ -21,6 +21,22 @@
   - `npm run test-nonrepeat`
 */
 function nonrepeat(str) {
-  // Your code here
+  let freq={};
+  let ans="";
+  for(let s of str){
+    freq[s]=(freq[s]||0)+1;
+  }
+
+  for(let s of str){
+    if(freq[s]==1){
+      ans+=s;
+      break;
+    }
+  }
+  if(ans==""){
+    return null;
+  }
+  return ans;
+
 }
 module.exports = nonrepeat;

js-built-ins/problems/medium/primeupto100.js

@@ -16,7 +16,21 @@
 */
 
 function getPrimesUpTo100() {
-  // Your code here
+  let arr=[];
+  for(let i=2; i<=100; i++){
+    let isPrime=true;
+
+    for(let j=2; j*j<=i; j++){
+      if(i%j==0){
+        isPrime=false;
+        break
+      }
+    }
+    if(isPrime){
+      arr.push(i);
+    }
+  }
+  return arr;
 }
 
 module.exports = { getPrimesUpTo100 };

js-built-ins/problems/medium/reverseInteger.js

@@ -22,7 +22,20 @@
 */
 
 function reverseInteger(num) {
-  // Your code here
+
+  let s = String(num);
+  let sign=1;
+  if(s[0]=='-'){
+    sign=-1;
+    s=s.slice(1);
+  }
+  let ns=s.split("").reverse().join("");
+
+  let ans=Number(ns);
+  ans*=sign;
+
+  return ans;
+
 }
 
 module.exports = reverseInteger;

js-built-ins/problems/medium/stringCompression.js

@@ -20,8 +20,24 @@
   Once you've implemented the logic, test your code by running
   - `npm run test-compressString`
 */
-function compression(str) {
-  // Your code here
+
+function compression(s){
+  let n=s.length;
+  let cnt=0;
+  let ans="";
+
+  for(let i=0; i<n; i++){
+    cnt++;
+    if(s[i]!==s[i+1]){
+      ans+=s[i];
+      if(cnt>1){
+        ans+=cnt;
+      }
+      cnt=0;
+    }
+  }
+
+  return ans;
 }
 
 module.exports = compression;