6f48cab072
14_sorts => 13_sorts, since the counting sort algorithm was introduced in the 13th lecture.
54 lines
1.1 KiB
Java
54 lines
1.1 KiB
Java
package sorts;
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/**
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* 计数排序
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*
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* Author: ZHENG
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*/
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public class CountingSort {
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// 计数排序，a是数组，n是数组大小。假设数组中存储的都是非负整数。
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public static void countingSort(int[] a, int n) {
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if (n <= 1) return;
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// 查找数组中数据的范围
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int max = a[0];
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for (int i = 1; i < n; ++i) {
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if (max < a[i]) {
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max = a[i];
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}
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}
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// 申请一个计数数组c，下标大小[0,max]
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int[] c = new int[max + 1];
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for (int i = 0; i < max + 1; ++i) {
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c[i] = 0;
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}
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// 计算每个元素的个数，放入c中
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for (int i = 0; i < n; ++i) {
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c[a[i]]++;
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}
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// 依次累加
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for (int i = 1; i < max + 1; ++i) {
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c[i] = c[i-1] + c[i];
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}
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// 临时数组r，存储排序之后的结果
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int[] r = new int[n];
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// 计算排序的关键步骤了，有点难理解
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for (int i = n - 1; i >= 0; --i) {
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int index = c[a[i]]-1;
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r[index] = a[i];
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c[a[i]]--;
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}
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// 将结果拷贝会a数组
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for (int i = 0; i < n; ++i) {
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a[i] = r[i];
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}
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}
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}
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