solve 191: number of 1 bits

Author: andavid

vscode/191.number-of-1-bits.java

@@ -0,0 +1,77 @@
+/*
+ * @lc app=leetcode id=191 lang=java
+ *
+ * [191] Number of 1 Bits
+ *
+ * https://leetcode.com/problems/number-of-1-bits/description/
+ *
+ * algorithms
+ * Easy (42.02%)
+ * Total Accepted:    250K
+ * Total Submissions: 586.7K
+ * Testcase Example:  '00000000000000000000000000001011'
+ *
+ * Write a function that takes an unsigned integer and return the number of '1'
+ * bits it has (also known as the Hamming weight).
+ * 
+ * 
+ * 
+ * Example 1:
+ * 
+ * 
+ * Input: 00000000000000000000000000001011
+ * Output: 3
+ * Explanation: The input binary string 00000000000000000000000000001011 has a
+ * total of three '1' bits.
+ * 
+ * 
+ * Example 2:
+ * 
+ * 
+ * Input: 00000000000000000000000010000000
+ * Output: 1
+ * Explanation: The input binary string 00000000000000000000000010000000 has a
+ * total of one '1' bit.
+ * 
+ * 
+ * Example 3:
+ * 
+ * 
+ * Input: 11111111111111111111111111111101
+ * Output: 31
+ * Explanation: The input binary string 11111111111111111111111111111101 has a
+ * total of thirty one '1' bits.
+ * 
+ * 
+ * 
+ * Note:
+ * 
+ * 
+ * Note that in some languages such as Java, there is no unsigned integer type.
+ * In this case, the input will be given as signed integer type and should not
+ * affect your implementation, as the internal binary representation of the
+ * integer is the same whether it is signed or unsigned.
+ * In Java, the compiler represents the signed integers using 2's complement
+ * notation. Therefore, in Example 3 above the input represents the signed
+ * integer -3.
+ * 
+ * 
+ * 
+ * 
+ * Follow up:
+ * 
+ * If this function is called many times, how would you optimize it?
+ * 
+ */
+public class Solution {
+  // you need to treat n as an unsigned value
+  public int hammingWeight(int n) {
+    int count = 0;
+    while (n != 0) {
+      n = n & (n - 1);
+      count++;
+    }
+    return count;
+  }
+}
+