leetcode week2-2

Author: bus710

counting-bits/bus710.rs

@@ -0,0 +1,34 @@
+// T: O(n log n)
+// S: O(n)
+
+pub fn count_bits(n: i32) -> Vec<i32> {
+    // Prepare a vector.
+    // The first item can just be 0
+    let mut vec = Vec::from([0]);
+
+    // Iterate as many as the given number + 1 
+    for num in 1..n + 1 {
+        // Get a binary string from the number (ex: 2 => 10)
+        let num_str = format!("{num:b}");
+        // Count '1' from the given binary string
+        let cnt = num_str.chars().filter(|c| *c == '1').count();
+        // Store the number in the vector
+        vec.push(cnt as i32);
+    }
+
+    vec
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn it_works() {
+        let result = count_bits(2);
+        assert_eq!(result, Vec::from([0, 1, 1]));
+
+        let result2 = count_bits(5);
+        assert_eq!(result2, Vec::from([0, 1, 1, 2, 1, 2]));
+    }
+}