codechash
diff --git a/‎Basics/index.js‎
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+/*
+Question 1: sum of all natural numbers from 1 to n
+
+sum of 1 to 5: 15
+*/
+
+function sumOfNaturalNumber(num){
+    let sum = 0;
+    for(let i=1; i<=num; i++){
+        sum = sum + i;
+    }
+    return sum;
+}
+
+console.log(sumOfNaturalNumber(5)) //15
+console.log(sumOfNaturalNumber(10)) //55
+console.log(sumOfNaturalNumber(8)) //36
+
+
+/*
+Question 2: Sum of digits of a number
+
+1287: 1+2+8+7 = 18
+
+*/
+
+function sumOfDigits(num){
+    let sum = 0;
+    while(num > 0){
+        sum += num%10;
+        num = Math.floor(num / 10);
+    }
+    return sum;
+}
+
+console.log(sumOfDigits(1287)) //18
+
+/*
+Question 3: count the number of digits of a number
+34252: 5
+-121 = 3
+*/
+
+function countDigits(num){
+    num = Math.abs(num);
+    let count = 0;
+    do {
+        count++;
+        num = Math.floor(num / 10);
+    } while (num > 0);
+    return count;
+}
+
+console.log(countDigits(121)) //3
+console.log(countDigits(-1211413131)) //10
+
+/*
+Question 4: Given an integer x, return true if x is a palindrome, and false otherwise.
+
+A palindrome number is a number that remains the same when digits are reversed
+*/
+
+let isPalindrome = function(x) {
+    let copyNum = x, reverseNum = 0;
+
+    while(copyNum > 0){
+        const lastDigit = copyNum%10;
+        reverseNum = reverseNum*10 + lastDigit;
+        copyNum = Math.floor(copyNum/10)
+    }
+
+    return x === reverseNum
+};
+
+console.log(isPalindrome(121)) //true
+console.log(isPalindrome(1234)) //false
+
+/*
+Question 5: Find nth fibonacci number
+
+The Fibonacci numbers, commonly denoted F(n) form a sequence, called the Fibonacci sequence, such that each number is the sum of the two preceding ones, starting from 0 and 1
+
+Fibonacci Sequence: 0 1 1 2 3 5 8...
+*/
+
+let fib = function(n) {
+    if(n < 2){
+        return n;
+    }
+
+    let prev = 0, curr = 1, next;
+    for(let i=2; i<= n; i++){
+        next = prev + curr;
+        prev = curr;
+        curr = next;
+    }
+    return next;
+};
+
+console.log(fib(5)) // 5
+console.log(fib(10)) //55
+
+/*
+Question 6: Missing Number
+
+Given an array nums containing n distinct numbers in the range [0, n], return the only number in the range that is missing from the array.
+*/
+
+let missingNumber = function(nums) {
+    let sum = 0;
+    for(let i=0; i<nums.length; i++){
+        sum += nums[i];
+    }
+    return nums.length*(nums.length+1)/2 - sum;
+};
+
+/*
+One Line Solution: 
+
+let missingNumber = (nums) => nums.length*(nums.length+1)/2 - nums.reduce((acc, num) => num + acc);
+*/
+
+console.log(missingNumber([3,0,1])) //2
+console.log(missingNumber([9,6,4,2,3,5,7,0,1])) //8