Merge pull request #93 from nhistory/week4

[Sehwan]Week4 solutions with javascript

Author: leokim0922

counting-bits/nhistory.js

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+var countBits = function (n) {
+  // Create array which has 0 element length of n
+  const dp = new Array(n + 1).fill(0);
+  let offset = 1;
+
+  for (let i = 1; i <= n; i++) {
+    if (offset * 2 === i) offset = i;
+    dp[i] = 1 + dp[i - offset];
+  }
+  return dp;
+};
+
+/**
+      0 -> 0000 -> dp[0] = 0
+      1 -> 0001 -> dp[1] = 1 + dp[1-1] = 1
+      2 -> 0010 -> dp[2] = 1 + dp[2-2] = 1
+      3 -> 0011 -> dp[3] = 1 + dp[3-2] = 2
+      4 -> 0100 -> dp[4] = 1 + dp[4-4] = 1
+      5 -> 0101 -> dp[5] = 1 + dp[5-4] = 2
+      6 -> 0110 -> dp[6] = 1 + dp[6-4] = 2
+      7 -> 0111 -> dp[7] = 1 + dp[7-4] = 3
+      8 -> 1000 -> dp[8] = 1 + dp[8-8] = 1
+   */
+
+// TC: O(n)
+// SC: O(1)

group-anagrams/nhistory.js

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+var groupAnagrams = function (strs) {
+  // Declare hash map to store sorted strs
+  let map = new Map();
+
+  for (let str of strs) {
+    // Sorted each str
+    const sortedStr = str.split("").sort().join("");
+
+    // If there is alread sortedStr on the map, pushed str
+    if (map.has(sortedStr)) {
+      map.get(sortedStr).push(str);
+    } else {
+      // If there is no sortedStr on the map, insert [str]
+      map.set(sortedStr, [str]);
+    }
+  }
+  return Array.from(map.values());
+};
+
+// TC: O(n*klogk)
+// SC: O(n*k)
+// n -> length of strs array
+// k -> amount of character for each element

missing-number/nhistory.js

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+var missingNumber = function (nums) {
+  // Get a expected summation
+  const n = nums.length;
+  const expectedSum = (n * (n + 1)) / 2;
+
+  // Calculate summation of nums
+  let numsSum = 0;
+  for (let i = 0; i < n; i++) {
+    numsSum += nums[i];
+  }
+
+  return expectedSum - numsSum;
+};
+
+// TC: O(n)
+// SC: O(1)

number-of-1-bits/nhistory.js

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+var hammingWeight = function (n) {
+  let count = 0;
+  while (n) {
+    // Check rightmost bit is equal to 1 by using bitwise AND operator
+    count += n & 1;
+    // Remove rightmost bit from n by using right shift operator
+    n >>= 1;
+  }
+  return count;
+};
+
+// TC: O(1) -> The worst case of 32-integer would be O(32)
+// SC: O(1)

reverse-bits/nhistory.js

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+var reverseBits = function (n) {
+  // Make variable to store input
+  // toString method doesn't include 0 front of number
+  let binary = n.toString(2);
+
+  // Added number of 0s to satisfy 32 bits
+  while (binary.length < 32) {
+    binary = "0" + binary;
+  }
+
+  // Reversed binary string and convert into integer
+  return parseInt(binary.split("").reverse().join(""), 2);
+};
+
+// TC: O(1)
+// SC: O(1)