今日算法题

import java.util.*;public class test_04_15 {//合并两个有序数组public void merge(int[] nums1, int m, int[] nums2, int n) {int nm = nums1.length-1;int i=m-1;int j=n-1;while (i>=0&&j>=0) {if (nums1[i] > nums2[j]) {nums1[nm--] = nums1[i--];} else {nums1[nm--] = nums2[j--];}}while (i>=0){nums1[nm--] = nums1[i--];}while (j>=0){nums1[nm--] = nums2[j--];}}//无重复字符的最长子串//abcabcbbpublic static int lengthOfLongestSubstring(String s) {if (s.length()==0){return 0;}int start=0;int end=0;int maxRes = 1;HashMap<Character,Integer> hashMap = new HashMap<>();while (end<s.length()){//不存在重复if (hashMap.containsKey(s.charAt(end))&&hashMap.get(s.charAt(end))>=start){//存在重复的start=hashMap.get(s.charAt(end))+1;}else{maxRes=Math.max(maxRes,end-start+1);hashMap.put(s.charAt(end),end);end++;}}return maxRes;}//判断子序列public boolean isSubsequence(String s, String t) {int i=0;int j=0;while (j<t.length()) {if (s.charAt(i) == t.charAt(j)) {i++;}j++;}return i==s.length();}//删除有序数组中的重复项//1 1 2 3public static int removeDuplicates(int[] nums){int i=0;int j=0;while (j<nums.length-1){if (nums[j]==nums[j+1]){j++;}else{nums[i]=nums[j];i++;j++;}}nums[i++]=nums[j];return i;}public static int maxArea(int[] height) {int start = 0;int end = height.length-1;int cap = 0;while (start<end){cap = Math.max(cap,Math.min(height[start],height[end])*(end-start));if (height[start]<height[end]){start++;}else{end--;}}return cap;}//三数之和public static List<List<Integer>> threeSum(int[] nums) {Arrays.sort(nums);System.out.println(Arrays.toString(nums));List<List<Integer>> res = new ArrayList<>();for (int i=0;i<nums.length;i++){//获取第一个数int temp1 = -nums[i];int j=0;int k=nums.length-1;while (j<k){if (j==i){j++;continue;}if (k==i){k--;continue;}if (nums[j]+nums[k]<temp1){j++;}else if (nums[j]+nums[k]>temp1){k--;}else{List<Integer> list = Arrays.asList(nums[i], nums[j], nums[k]);Collections.sort(list);if (!res.contains(list)){res.add(list);}j++;k--;}}}return res;}//[-1,0,1,2,-1,-4]//[-4,-1,-1,0,1,5]public static List<List<Integer>> threeSum2(int[] nums) {List<List<Integer>> res = new ArrayList<>();Arrays.sort(nums);System.out.println(Arrays.toString(nums));for (int i=0;i<nums.length-2;i++){//跳过重复数字if (i>0&&nums[i]==nums[i-1]){continue;}int j=i+1;int k=nums.length-1;while (j<k){if (nums[j]+nums[k]==-nums[i]){res.add(Arrays.asList(nums[i],nums[j],nums[k]));//去除重复的while (j<k&&nums[j]==nums[j+1]){j++;}while (j<k&&nums[k]==nums[k-1]){k--;}j++;k--;}else if (nums[j]+nums[k]>-nums[i]){k--;}else{j++;}}}return res;}//反转链表public ListNode reverseList(ListNode head) {ListNode pre = null;ListNode p =head;ListNode pp=p.next;while (pp!=null){p.next=pre;pre=p;p=pp;pp=pp.next;}p.next=pre;return p;}// 1 2public ListNode reverseList2(ListNode head) {if (head.next==null){return head;}ListNode newHead = reverseList2(head.next);head.next.next=head;head.next=null;return newHead;}//环形链表public boolean hasCycle(ListNode head) {ListNode slow = head;ListNode quick = head;while (quick!=null&&quick.next!=null){slow=slow.next;quick=quick.next.next;if (slow==quick){return true;}}return false;}//反转链表IIpublic static ListNode reverseBetween(ListNode head, int left, int right) {ListNode rightNode = head;ListNode leftNode = head;ListNode leftNodePre = null;while (left-->1){leftNodePre=leftNode;leftNode=leftNode.next;}while (right-->1){rightNode=rightNode.next;}ListNode copyLeftNode = leftNode;// 1 2 3 4 5ListNode pre = null;ListNode p=leftNode;ListNode pp=p.next;while (p!=rightNode){p.next=pre;pre=p;p=pp;pp=pp.next;}p.next=pre;copyLeftNode.next=pp;if (leftNodePre==null){return p;}else{leftNodePre.next=p;return head;}}//k个一组反转链表public static ListNode reverseKGroup(ListNode head, int k) {int count = 0;ListNode p = head;while (p!=null){count++;p=p.next;}int left=1;for (int i=0;i<count/k;i++){head = reverseBetween(head, left, left + k - 1);left=left+k;}return head;}//删除链表中的节点public void deleteNode(ListNode node) {node.val=node.next.val;node.next=node.next.next;}public ListNode deleteNode2(ListNode head,ListNode node) {ListNode dumpy = new ListNode(-1);dumpy.next=head;ListNode nodePre = dumpy;while (nodePre.next!=node){nodePre=nodePre.next;}nodePre.next=node.next;return dumpy.next;}//重排链表//1 2//5 4 3public static void reorderList(ListNode head) {//找出中间节点ListNode slow = head;ListNode quick = head;ListNode slowPre = null;while (quick!=null&&quick.next!=null){slowPre = slow;slow= slow.next;quick=quick.next.next;}if (slowPre==null){return;}else{slowPre.next=null;}//将后面链表进行反转ListNode pre = null;ListNode p = slow;ListNode pp=slow.next;while (pp!=null){p.next=pre;pre = p;p=pp;pp=pp.next;}p.next=pre;//开始进行合并//1 2//4 3ListNode l1 = head;ListNode l2 = p;ListNode l2Pre;ListNode.printList(l1);ListNode.printList(l2);while (l1!=null){l2Pre=l2;l2=l2.next;l2Pre.next=l1.next;l1.next=l2Pre;l1=l1.next.next;}if (l2!=null){p=head;while (p.next!=null){p=p.next;}p.next=l2;}}//删除链表倒数第n个节点public ListNode removeNthFromEnd(ListNode head, int n) {ListNode pre = null;ListNode p = head;ListNode temp = head;while (n-->0){temp=temp.next;}while (temp!=null){temp=temp.next;pre=p;p=p.next;}if (pre==null){return head.next;}else{pre.next=pre.next.next;}return head;}//旋转链表public ListNode rotateRight(ListNode head, int k) {if (head==null||head.next==null){return head;}int count = 1;ListNode newHead = new ListNode(head.val);ListNode q=newHead;ListNode p = head.next;ListNode pre = head;while (p!=null){q.next=new ListNode(p.val);q=q.next;pre=p;p=p.next;count++;}pre.next=newHead;int num = count-(k%count);p=head;while (num-->0){p=p.next;}ListNode right = p;while (--count>0){right=right.next;}right.next=null;return p;}public static void main(String[] args) {ListNode head1 = new ListNode(1);ListNode head2 = new ListNode(2);ListNode head3 = new ListNode(3);head1.next=head2;head2.next=head3;reorderList(head1);ListNode.printList(head1);}
}