Create file

Author: bugsweeper

Diff for: 1415-Thek-thLexicographicalStringofAllHappyStringsofLengthn/1415-Thek-thLexicographicalStringofAllHappyStringsofLengthn.rs

@@ -0,0 +1,26 @@
+const RELATIVE_SHIFT: [[usize;2];3] = [
+    [1, 2],
+    [0, 2],
+    [0, 1]
+];
+
+impl Solution {
+    pub fn get_happy_string(n: i32, k: i32) -> String {
+        if k > (1 << (n - 1)) * 3 {
+            return String::new();
+        }
+        let mut result = Vec::with_capacity(n as usize);
+        let mut combinations = 1_usize << (n - 1);
+        let mut previous_shift = (k as usize - 1) / combinations;
+        let mut k = (k as usize - 1) % combinations;
+        result.push(previous_shift as u8 + b'a');
+        for i in 0..n - 1 {
+            combinations >>= 1;
+            let shift = RELATIVE_SHIFT[previous_shift][k / combinations];
+            result.push(shift as u8 + b'a');
+            k %= combinations;
+            previous_shift = shift;
+        }
+        unsafe{String::from_utf8_unchecked(result)}
+    }
+}