Add Pigeonhole Sort Algorithm in R (#234)

Author: Siddhram

sorting_algorithms/pigeonhole_sort.r

@@ -0,0 +1,51 @@
+# Pigeonhole Sort Function
+# Sorts an integer vector using the Pigeonhole Sort algorithm.
+# Parameters:
+# - arr: Input integer vector to be sorted.
+# Returns:
+# - Sorted vector.
+
+pigeonhole_sort <- function(arr) {
+  # Handle empty input
+  if (length(arr) == 0) return(arr)
+  
+  # Pigeonhole sort is defined for integers
+  if (!all(arr == floor(arr))) {
+    stop("pigeonhole_sort works with integer values only.")
+  }
+  
+  # Find range
+  min_val <- min(arr)
+  max_val <- max(arr)
+  range <- as.integer(max_val - min_val + 1L)
+  
+  # Create holes (counts per value)
+  holes <- integer(range)
+  
+  # Populate holes
+  for (i in seq_along(arr)) {
+    holes[arr[i] - min_val + 1L] <- holes[arr[i] - min_val + 1L] + 1L
+  }
+  
+  # Reconstruct sorted array
+  idx <- 1L
+  for (i in seq_len(range)) {
+    cnt <- holes[i]
+    if (cnt > 0L) {
+      val <- (i - 1L) + min_val
+      arr[idx:(idx + cnt - 1L)] <- val
+      idx <- idx + cnt
+    }
+  }
+  
+  return(arr)
+}
+
+# Example usage:
+# ---------------
+# Input:  c(8, 3, 2, 7, 4, 6, 8)
+# Output: c(2, 3, 4, 6, 7, 8, 8)
+
+elements_vec <- c(8, 3, 2, 7, 4, 6, 8)
+sorted_vec <- pigeonhole_sort(elements_vec)
+print(sorted_vec)