Count bits

Author: ratulb

count_bits/Cargo.toml

@@ -0,0 +1,6 @@
+[package]
+name = "count_bits"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]

count_bits/src/lib.rs

@@ -0,0 +1,30 @@
+pub fn count_bits(n: usize) -> Vec<usize> {
+    let mut result = Vec::with_capacity(n + 1);
+    result.push(0);
+    let mut power = 1;
+    for i in 1..=n {
+        if i == power * 2 {
+            power = i;
+        }
+        result.insert(i, 1 + result[i - power]);
+    }
+    println!("{:?}", result);
+    return result;
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_count_bits_1() {
+        let result = count_bits(2);
+        assert_eq!(result, vec![0, 1, 1]);
+    }
+
+    #[test]
+    fn test_count_bits_2() {
+        let result = count_bits(5);
+        assert_eq!(result, vec![0, 1, 1, 2, 1, 2]);
+    }
+}

src/SUMMARY.md

@@ -56,3 +56,7 @@
 * [Product except self](./product_except_self/introduction.md)
 * [Max sub array sum](./max_sub_array_sum/introduction.md)
 * [Max vowels in substring](./maximum-number-of-vowels/introduction.md)
+* [Count bits](./count_bits/introduction.md)
+
+
+

src/count_bits/introduction.md

@@ -0,0 +1,20 @@
+# Count 1s For Each Entry
+ Return an array where each element at index i (0 ≤ i ≤ n) is the number of 1's in the binary representation of i.
+
+
+```rust,ignore
+pub fn count_bits(n: usize) -> Vec<usize> {
+    let mut result = Vec::with_capacity(n + 1);
+    result.push(0);
+    let mut power = 1;
+    for i in 1..=n {
+        if i == power * 2 {
+            power = i;
+        }
+        result.insert(i, 1 + result[i - power]);
+    }
+    return result;
+}
+
+```
+[Source](https://github.com/ratulb/programming_problems_in_rust/blob/master/count_bits/src/lib.rs)