feat: added JS solutions of 190, 268, 371

Author: MarinaPotovichenko

javascript/190-Reverse-Bits.js

@@ -0,0 +1,13 @@
+var reverseBits = function(n) {
+    let result = 0b0;
+    let curr = n;
+
+    for (let i = 0; i < 32; i++) {
+        const lastBit = curr & 0b1;
+        result = result << 1;
+        result = result | lastBit;
+        curr = curr >> 1;
+    }
+
+    return result >>> 0;
+};

javascript/268-Missing-Number.js

@@ -0,0 +1,19 @@
+var missingNumberWithSums = function (nums) {
+    let res = nums.length;
+
+    for(let i = 0; i < nums.length; i++) {
+        res += i - nums[i];
+    }
+
+    return res;
+};
+
+var missingNumberWithBit = function (nums) {
+    let res = nums.length;
+
+    for(let i = 0; i < nums.length; i++) {
+        res = res ^ i ^ nums[i];
+    }
+
+    return res;
+};

javascript/371-Sum-of-Two-Integers.js

@@ -0,0 +1,12 @@
+var getSum = function(a, b) {
+    let tb = b;
+    let res = a;
+
+    while(tb) {
+        let temp = (res & tb) << 1;
+        res = res ^ tb;
+        tb = temp;
+    }
+
+    return res;
+};