Add problem 1009

Author: avhn

algorithms/1009/README.md

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+## 1009. Complement of Base 10 Integer
+
+Every non-negative integer `N` has a binary representation. For example, `5` can be represented as `"101"` in binary, 11 as "1011" in binary, and so on. Note that except for `N = 0`, there are no leading zeroes in any binary representation.
+
+The *complement* of a binary representation is the number in binary you get when changing every `1` to a `0` and `0` to a `1`. For example, the complement of `"101"` in binary is `"010"` in binary.
+
+For a given number `N` in base-10, return the complement of it's binary representation as a base-10 integer.
+
+<br>
+
+**Example 1:**
+<pre>
+<b>Input:</b> 5
+<b>Output:</b> 2
+<b>Explanation:</b> 5 is "101" in binary, with complement "010" in binary, which is 2 in
+base-10.
+</pre>
+
+**Example 2:**
+<pre>
+<b>Input:</b> 7
+<b>Output:</b> 0
+<b>Explanation:<b> 7 is "111" in binary, with complement "000" in binary, which is 0 in base-10.
+</pre>
+
+**Example 3:**
+<pre>
+<b>Input:</b> 10
+<b>Output:</b> 5
+<b>Explanation:</b> 10 is "1010" in binary, with complement "0101" in binary, which is 5 in base-10.
+ </pre>
+
+**Note:**
+ 1. `0 <= N < 10^9`
+ 2. This question is the same as 476: https://leetcode.com/problems/number-complement/`

algorithms/1009/solution.go

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+package main
+
+// Time and space complexity, O(1)
+func bitwiseComplement(N int) int {
+if N == 0 {
+return 1
+}
+var c int
+for m := 1; N != 0; m, N = m*2, N>>1 {
+if N&1 != 1 {
+c += m
+}
+}
+return c
+}