排序

数组的快速排序   nlogn   空间复杂度为log(n)     public static int partion(int [] a,int from,int to){        if(a==null) return -1;        int base=a[from];        while(from<to){            while(from<to&&a[to]>base){                to--;            }            if(from<to){                a[from++]=a[to];            }            while(from<to&&a[from]<base){                from++;            }            if(from<to){                a[to--]=a[from];            }        }        a[from]=base;        return from;    }    public static void fastSort(int [] a,int low,int high){        if(low>high||a==null) return;        if(low<=high){            int index=partion(a,low,high);            fastSort(a,low,index-1);            fastSort(a,index+1,high);        }    }链表的快速排序  nlogn  空间复杂度是logn    public ListNode sortList(ListNode head) {        if (head == null || head.next == null) {            return head;        }        ListNode dummy1 = new ListNode(0);        ListNode dummy2 = new ListNode(0);        ListNode prev1 = dummy1;        ListNode prev2 = dummy2;        ListNode node = head.next;        ListNode prev = head;        while (node != null) {            if (node.val < head.val) {                prev1.next = node;                prev1 = prev1.next;            } else if (node.val > head.val) {                prev2.next = node;                prev2 = prev2.next;            } else {                prev.next = node;                prev = prev.next;            }            node = node.next;        }        prev1.next = prev2.next = prev.next = null;        dummy1.next = sortList(dummy1.next);        dummy2.next = sortList(dummy2.next);        prev1 = dummy1;        while (prev1.next != null) {            prev1 = prev1.next;        }        prev1.next = head;        prev.next = dummy2.next;        return dummy1.next;    }归并排序    nlogn    空间是o(n)        public static void merge(int[] a, int from, int mid, int to) {        if (from >= to)            return;        int[] save = new int[to - from + 1];        int i = from, j = mid + 1, k = 0;        while (i <= mid && j <= to) {            if (a[i] <= a[j]) {                save[k++] = a[i++];            } else                save[k++] = a[j++];        }        while (i <= mid) {            save[k++] = a[i++];        }        while (j <= to) {            save[k++] = a[j++];        }        for (int k2 = 0; k2 < save.length; k2++) {            a[from + k2] = save[k2];        }    }    public static void sort(int[] a, int from, int to) {        if (from >= to || a == null)            return;        int mid = from + (to - from) / 2;        if (from < to) {            sort(a, from, mid);            sort(a, mid + 1, to);            merge(a, from, mid, to);        }    }链表的归并排序    public ListNode sortList(ListNode head) {        if(head==null||head.next==null) return head;        ListNode fast=fast.next.next,slow=head;        while(fast!=null&&fast.next!=null){            fast=fast.next.next;            slow=slow.next;        }        fast=slow.next;        slow.next=null;        ListNode p1=sortList(fast);        ListNode p2=sortList(head);        return merge(p1,p2);       }    public ListNode merge(ListNode l1,ListNode l2){        if(l1==null) return l2;        if(l2==null) return l1;        ListNode dump=new ListNode(0);        ListNode p=dump;        while(l1!=null&&l2!=null){            if(l1.val<l2.val){                p.next=l1;                p=p.next;                l1=l1.next;            }            else{                p.next=l2;                l2=l2.next;                p=p.next;            }        }               while(l1!=null){            p.next=l1;                p=p.next;                l1=l1.next;        }        while(l2!=null){            p.next=l2;                l2=l2.next;                p=p.next;        }        return dump.next;       }数组的插入排序  O（n2）      public static void insertSort(int [] a){        if(a.length<=1) return;        for(int i=1;i<a.length;i++){            int tmp=a[i];            int j=i-1;            while(j>=0&&a[j]>tmp){                a[j+1]=a[j];                j--;            }            a[j+1]=tmp;        }    }链表的插入排序从左向右找到第一个大于当前值的位置，放到其前面，根据链表的特点，要比较.next.val，这样才能放到其前面改进点是不一定每次都需要从头开始找，只有点高当前值比排好的最后一位小的时候才需要    public static ListNode insertSort(ListNode head){        if(head==null||head.next==null) return head;        ListNode dump=new ListNode(0);        ListNode p=dump,cur=head;//p是辅助，cur是当前开始排哪个了        while(cur!=null){            if(p!=dump&&p.val>cur.val){                p=dump;            }            while(p.next!=null&&cur.val>=p.next.val){                p=p.next;            }            ListNode tmp=cur.next;            cur.next=p.next;            p.next=cur;            cur=tmp;//移位            }        return dump.next;    }