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libft/sorting/ft_radixsort.c

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+/* ************************************************************************** */
+/*                                                                            */
+/*                                                        :::      ::::::::   */
+/*   ft_radixsort.c                                     :+:      :+:    :+:   */
+/*                                                    +:+ +:+         +:+     */
+/*   By: thrieg <thrieg@student.42mulhouse.fr>      +#+  +:+       +#+        */
+/*                                                +#+#+#+#+#+   +#+           */
+/*   Created: 2024/11/18 14:18:55 by alier             #+#    #+#             */
+/*   Updated: 2025/02/16 19:06:42 by thrieg           ###   ########.fr       */
+/*                                                                            */
+/* ************************************************************************** */
+
+#include <stdlib.h>
+#include <stdbool.h>
+#include "ft_sorting.h"
+
+static void	ft_naive_countsort2(struct s_countsort cs)
+{
+	size_t	i;
+
+	i = cs.size - 1;
+	while (true)
+	{
+		cs.tmp[cs.count[(cs.a[i] / cs.exp) % 10] - 1] = cs.a[i];
+		cs.count[(cs.a[i] / cs.exp) % 10]--;
+		if (i == 0)
+			break ;
+		i--;
+	}
+	ft_memcpy(cs.a, cs.tmp, cs.size * sizeof(*cs.a));
+}
+
+/*
+ * used by `ft_naive_radixsort`
+ */
+static void	ft_naive_countsort(size_t size, unsigned int a[size],
+							unsigned int exp)
+{
+	unsigned int	*tmp;
+	unsigned int	count[10];
+	size_t			i;
+
+	tmp = malloc(size * sizeof(unsigned int));
+	ft_bzero(count, 10 * sizeof(unsigned int));
+	i = 0;
+	while (i < size)
+	{
+		count[(a[i] / exp) % 10]++;
+		i++;
+	}
+	i = 1;
+	while (i < 10)
+	{
+		count[i] += count[i - 1];
+		i++;
+	}
+	ft_naive_countsort2((struct s_countsort){size, a, exp, tmp, count});
+	free(tmp);
+}
+
+/*
+ * Worst-case performance:		O(size * max_digits)
+ * Worst-case space complexity:	O(size + max_digits)
+ */
+void	ft_naive_radixsort(size_t size, unsigned int a[size])
+{
+	unsigned int	m;
+	unsigned int	exp;
+
+	m = ft_max_uint(size, a);
+	exp = 1;
+	while (m / exp > 0)
+	{
+		ft_naive_countsort(size, a, exp);
+		exp *= 10;
+	}
+}