feat: number-of-1-bits solution

Author: sm9171

number-of-1-bits/sm9171.java

@@ -0,0 +1,8 @@
+public static int hammingWeight(int n) {
+    int sum = 0;
+    while (n > 0) {
+        sum += n % 2;
+        n /= 2;
+    }
+    return sum;
+}