feat: Add Burrows-Wheeler Transform (BWT) implementation in R

string_manipulation/burrows.R

@@ -0,0 +1,31 @@
+# Burrows-Wheeler Transform (BWT) in R
+# Computes the Burrows-Wheeler Transform of a string
+# Useful in compression and efficient substring searching
+
+burrows_wheeler_transform <- function(s) {
+  s <- paste0(s, "$")  # Append unique end-of-string character
+  n <- nchar(s)
+
+  # Generate all rotations of the string
+  rotations <- character(n)
+  for (i in 1:n) {
+    rotations[i] <- paste0(substr(s, i, n), substr(s, 1, i - 1))
+  }
+
+  # Sort the rotations lexicographically
+  rotations_sorted <- sort(rotations)
+
+  # Build BWT by taking the last character of each sorted rotation
+  bwt <- paste0(sapply(rotations_sorted, function(x) substr(x, n, n)), collapse = "")
+
+  return(list(original = s, rotations_sorted = rotations_sorted, bwt = bwt))
+}
+
+# Interactive input
+s <- readline(prompt = "Enter a string: ")
+result <- burrows_wheeler_transform(s)
+
+cat("Original string with end marker: ", result$original, "\n")
+cat("Sorted rotations:\n")
+print(result$rotations_sorted)
+cat("Burrows-Wheeler Transform: ", result$bwt, "\n")