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Code04_RadixSort.java
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package class08;
import java.util.Arrays;
public class Code04_RadixSort {
// only for no-negative value
public static void radixSort(int[] arr) {
if (arr == null || arr.length < 2) {
return;
}
radixSort(arr, 0, arr.length - 1, maxbits(arr));
}
public static int maxbits(int[] arr) {
int max = Integer.MIN_VALUE;
for (int i = 0; i < arr.length; i++) {
max = Math.max(max, arr[i]);
}
int res = 0;
while (max != 0) {
res++;
max /= 10;
}
return res;
}
// arr[L..R]排序 , 最大值的十进制位数digit
public static void radixSort(int[] arr, int L, int R, int digit) {
final int radix = 10;
int i = 0, j = 0;
// 有多少个数准备多少个辅助空间
int[] help = new int[R - L + 1];
for (int d = 1; d <= digit; d++) { // 有多少位就进出几次
// 10个空间
// count[0] 当前位(d位)是0的数字有多少个
// count[1] 当前位(d位)是(0和1)的数字有多少个
// count[2] 当前位(d位)是(0、1和2)的数字有多少个
// count[i] 当前位(d位)是(0~i)的数字有多少个
int[] count = new int[radix]; // count[0..9]
for (i = L; i <= R; i++) {
// 103 1 3
// 209 1 9
j = getDigit(arr[i], d);
count[j]++;
}
for (i = 1; i < radix; i++) {
count[i] = count[i] + count[i - 1];
}
for (i = R; i >= L; i--) {
j = getDigit(arr[i], d);
help[count[j] - 1] = arr[i];
count[j]--;
}
for (i = L, j = 0; i <= R; i++, j++) {
arr[i] = help[j];
}
}
}
public static int getDigit(int x, int d) {
return ((x / ((int) Math.pow(10, d - 1))) % 10);
}
// for test
public static void comparator(int[] arr) {
Arrays.sort(arr);
}
// for test
public static int[] generateRandomArray(int maxSize, int maxValue) {
int[] arr = new int[(int) ((maxSize + 1) * Math.random())];
for (int i = 0; i < arr.length; i++) {
arr[i] = (int) ((maxValue + 1) * Math.random());
}
return arr;
}
// for test
public static int[] copyArray(int[] arr) {
if (arr == null) {
return null;
}
int[] res = new int[arr.length];
for (int i = 0; i < arr.length; i++) {
res[i] = arr[i];
}
return res;
}
// for test
public static boolean isEqual(int[] arr1, int[] arr2) {
if ((arr1 == null && arr2 != null) || (arr1 != null && arr2 == null)) {
return false;
}
if (arr1 == null && arr2 == null) {
return true;
}
if (arr1.length != arr2.length) {
return false;
}
for (int i = 0; i < arr1.length; i++) {
if (arr1[i] != arr2[i]) {
return false;
}
}
return true;
}
// for test
public static void printArray(int[] arr) {
if (arr == null) {
return;
}
for (int i = 0; i < arr.length; i++) {
System.out.print(arr[i] + " ");
}
System.out.println();
}
// for test
public static void main(String[] args) {
int testTime = 500000;
int maxSize = 100;
int maxValue = 100000;
boolean succeed = true;
for (int i = 0; i < testTime; i++) {
int[] arr1 = generateRandomArray(maxSize, maxValue);
int[] arr2 = copyArray(arr1);
radixSort(arr1);
comparator(arr2);
if (!isEqual(arr1, arr2)) {
succeed = false;
printArray(arr1);
printArray(arr2);
break;
}
}
System.out.println(succeed ? "Nice!" : "Fucking fucked!");
int[] arr = generateRandomArray(maxSize, maxValue);
printArray(arr);
radixSort(arr);
printArray(arr);
}
}