Java常见排序算法怎么实现

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汇总：

1. 冒泡排序

每轮循环确定最值；

public void bubbleSort(int[] nums){    int temp;    boolean isSort = false; //优化，发现排序好就退出    for (int i = 0; i < nums.length-1; i++) {        for (int j = 0; j < nums.length-1-i; j++) {  //每次排序后能确定较大值            if(nums[j] > nums[j+1]){                isSort = true;                temp = nums[j];                nums[j] = nums[j+1];                nums[j+1] = temp;            }        }        if(!isSort){            return;        } else {            isSort = false;        }    }}

2. 选择排序

每次选出最值，再交换到边上；

public void selectSort(int[] nums){    for (int i = 0; i < nums.length-1; i++) {        int index = i;        int minNum = nums[i];        for (int j = i+1; j < nums.length; j++) {            if(nums[j] < minNum){                minNum = nums[j];                index = j;            }        }        if(index != i){            nums[index] = nums[i];            nums[i] = minNum;        }    }}

3. 插入排序

对循环的每个数找到属于自己的位置插入；

public void insertionSort(int[] nums){    for (int i = 1; i < nums.length; i++) {        int j = i;        int insertNum = nums[i];        while(j-1 >= 0 && nums[j-1] > insertNum){            nums[j] = nums[j-1];            j--;        }        nums[j] = insertNum;    }}

4. 快速排序

选一个基本值，小于它的放一边，大于它的放另一边；

public void quickSortDfs(int[] nums, int left, int right){    if(left > right){        return;    }    int l = left;    int r = right;    int baseNum = nums[left];    while(l < r){        //必须右边先走        while(nums[r] >= baseNum && l < r){            r--;        }        while(nums[l] <= baseNum && l < r){            l++;        }        int temp = nums[l];        nums[l] = nums[r];        nums[r] = temp;    }    nums[left] = nums[l];    nums[l] = baseNum;    quickSortDfs(nums, left, r-1);    quickSortDfs(nums, l+1, right);}

5. 归并排序

分治算法；

//归public void mergeSortDfs(int[] nums, int l, int r){    if(l >= r){        return;    }    int m = (l+r)/2;    mergeSortDfs(nums, l, m);    mergeSortDfs(nums, m+1, r);    merge(nums, l, m, r);}//并private void merge(int[] nums, int left, int mid, int right){    int[] temp = new int[right-left+1];    int l = left;    int m = mid+1;    int i = 0;    while(l <= mid && m <= right){        if(nums[l] < nums[m]){            temp[i++] = nums[l++];        } else {            temp[i++] = nums[m++];        }    }    while(l <= mid){        temp[i++] = nums[l++];    }    while(m <= right){        temp[i++] = nums[m++];    }    System.arraycopy(temp, 0, nums, left, temp.length);}

6. 希尔排序

引入步长减少数字交换次数提高效率；

6.1 希尔-冒泡排序（慢）

public void shellBubbleSort(int[] nums){    for (int step = nums.length/2; step > 0 ; step /= 2) {        for (int i = step; i < nums.length; i++) {            for (int j = i-step; j >= 0; j -= step) {                if(nums[j] > nums[j+step]){                    int temp = nums[j];                    nums[j] = nums[j+step];                    nums[j+step] = temp;                }            }        }    }}

6.2 希尔-插入排序（快）

public void shellInsertSort(int[] nums){    for (int step = nums.length/2; step > 0; step /= 2) {        for (int i = step; i < nums.length; i++) {            int j = i;            int insertNum = nums[i];            while(j-step >= 0 && nums[j-step] > insertNum){                nums[j] = nums[j-step];                j-=step;            }            nums[j] = insertNum;        }    }}

7. 堆排序

大顶堆实现升序，每次将最大值移到堆的最后一个位置上；

public void heapSort2(int[] nums) {    for(int i = nums.length/2-1; i >= 0; i--){        sift(nums, i, nums.length);    }    for (int i = nums.length-1; i > 0; i--) {        int temp = nums[0];        nums[0] = nums[i];        nums[i] = temp;        sift(nums, 0, i);    }}private void sift(int[] nums, int parent, int len) {    int value = nums[parent];    for (int child = 2*parent +1; child < len; child = child*2 +1) {        if(child+1 < len && nums[child+1] > nums[child]){            child++;        }        if(nums[child] > value){            nums[parent] = nums[child];            parent = child;        } else {            break;        }    }    nums[parent] = value;}

8. 计数排序

按顺序统计每个数出现次数；

public void countSort(int[] nums){    int max = Integer.MIN_VALUE;    int min = Integer.MAX_VALUE;    for(int num : nums){        max = Math.max(max, num);        min = Math.min(min, num);    }    int[] countMap = new int[max-min+1];    for(int num : nums){        countMap[num-min]++;    }    int i = 0;    int j = 0;    while(i < nums.length && j < countMap.length){        if(countMap[j] > 0){            nums[i] = j+min;            i++;            countMap[j]--;        } else {            j++;        }    }}

9. 桶排序

类似计数排序，不同点在于统计的是某个区间（桶）里的数；

public void bucketSort(int[] nums){    int max = Integer.MIN_VALUE;    int min = Integer.MAX_VALUE;    for(int num : nums){        max = Math.max(max, num);        min = Math.min(min, num);    }    int bucketCount = (max-min)/nums.length+1;    List> bucketList = new ArrayList<>();    for (int i = 0; i < bucketCount; i++) {        bucketList.add(new ArrayList<>());    }    for(int num : nums){        int index = (num-min)/nums.length;        bucketList.get(index).add(num);    }    for(List bucket : bucketList){        Collections.sort(bucket);    }    int j = 0;    for(List bucket : bucketList){        for(int num : bucket){            nums[j] = num;            j++;        }    }}

10. 基数排序

按个、十、百位依次归类排序；

public  void radixSort(int[] nums){    int min = Integer.MAX_VALUE;    int max = Integer.MIN_VALUE;    for (int num : nums) {        min = Math.min(min, num);        max = Math.max(max, num);    }    for (int i = 0; i < nums.length; i++) {        nums[i] -= min;    }    max -= min;    int maxLen = (max+"").length();    int[][] bucket = new int[nums.length][10];    int[] bucketCount = new int[10];    for (int i = 0, n = 1; i < maxLen; i++, n*=10) {        for (int num : nums) {            int digitVal = num / n % 10;            bucket[bucketCount[digitVal]][digitVal] = num;            bucketCount[digitVal]++;        }        int index = 0;        for (int j = 0; j < bucketCount.length; j++) {            if(bucketCount[j] > 0){                for (int k = 0; k < bucketCount[j]; k++) {                    nums[index] = bucket[k][j];                    index++;                }            }            bucketCount[j] = 0;        }    }    for (int i = 0; i < nums.length; i++) {        nums[i] += min;    }}

11. 使用集合或 API

11.1 优先队列

public void priorityQueueSort(int[] nums){    PriorityQueue queue = new PriorityQueue<>();    for(int num : nums){        queue.offer(num);    }    for (int i = 0; i < nums.length; i++) {        nums[i] = queue.poll();    }}

11.2 Java API

public void arraysApiSort(int[] nums){    Arrays.sort(nums);}

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