- Sort Colors:题目链接
方法1：计数排序
计数排序算法详情链接:点击这里
计数排序源码如下：1
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26import java.util.Arrays;
public class Solution1 {
// 时间复杂度O(N) 空间复杂度O(k) 其中K为要排序的数组的范围 O(3) 计数排序
public static void sortColors(int[] nums) {
// 1.创建计数数组 并初始化
int[] count = new int[3];
// 2.将nums元素存放进对应的count中计算出现次数
for (int i = 0; i < nums.length; ++i) {
count[nums[i]]++;
}
// 3.根据count出现次数来写入原数组nums
int j = 0;
for (int i = 0; i < count.length; ++i) {
while (count[i]-- != 0) {
nums[j++] = i;
}
}
}
public static void main(String[] args) {
int[] nums = {2, 0, 2, 1, 1, 0};
sortColors(nums);
System.out.println(Arrays.toString(nums));
}
}
方法2：三路快速排序
三路快速算法详情链接:点击这里
三路快速排序源码如下：1
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75import java.util.Arrays;
public class Solution2 {
public static void swap(int[] nums, int i, int j) {
int t = nums[i];
nums[i] = nums[j];
nums[j] = t;
}
public static void insertionSort(int[] nums, int left, int right) {
for (int i = left + 1; i <= right; ++i) {
int temp = nums[i];
int j = i;
for (; j > left && nums[j - 1] > temp; j--) {
nums[j] = nums[j - 1];
}
nums[j] = temp;
}
}
public static void quickSort3ways(int[] nums, int left, int right) {
if (right - left <= 15) {
insertionSort(nums, left, right);
return;
}
// 基准的选取 : 三路取中法
// 保证nums[left] <= nums[mid] <= nums[right] 最后将nums[left],nums[mid]交换
int mid = left + (right - left) / 2;
if (nums[left] > nums[mid]) {
swap(nums, left, mid);
}
if (nums[left] > nums[right]) {
swap(nums, left, right);
}
if (nums[mid] > nums[right]) {
swap(nums, mid, right);
}
swap(nums, left, mid);
// 基准的选取 : 随机数法
// swap(nums, left, (int)Math.random() * (right-left+1) + left );
int v = nums[left];
int lt = left;
int gt = right + 1;
int i = left + 1;
while (i < gt) {
if (nums[i] == v) {
i++;
} else if (nums[i] < v) {
swap(nums, i++, ++lt);
} else {
swap(nums, i, --gt);
}
}
swap(nums, left, lt--);
quickSort3ways(nums, left, lt);
quickSort3ways(nums, gt, right);
}
public static void sortColors(int[] nums) {
quickSort3ways(nums, 0, nums.length - 1);
}
public static void main(String[] args) {
int[] nums = {2, 0, 2, 1, 1, 0};
sortColors(nums);
System.out.println(Arrays.toString(nums));
}
}
ps：源代码链接