feat: 338. Counting Bits

counting-bits/HC-kang.ts

@@ -0,0 +1,26 @@
+// T.C: O(n)
+// S.C: O(n)
+function countBits(n: number): number[] {
+  // T.C: O(1)
+  // S.C: O(1)
+  function countBit(num: number): number {
+    num = num - ((num >>> 1) & 0x55555555);
+    num = (num & 0x33333333) + ((num >>> 2) & 0x33333333);
+    num = (num + (num >>> 4)) & 0x0f0f0f0f;
+    num = num + (num >>> 8);
+    num = num + (num >>> 16);
+    return num & 0x3f;
+  }
+
+  return new Array(n + 1).fill(0).map((_, i) => countBit(i));
+}
+
+// T.C: O(n)
+// S.C: O(n)
+function countBits(n: number): number[] {
+  const dp = new Array(n + 1).fill(0);
+  for (let i = 1; i <= n; i++) {
+    dp[i] = dp[i >> 1] + (i & 1);
+  }
+  return dp;
+}