1.数组部分

1.1二分查找

class Solution {public int search(int[] nums, int target) {if(nums.length==0)return -1;int l=0,r=nums.length-1;while(l<=r){int mid=l+r>>1;if(nums[mid]==target){return mid;}else if(nums[mid]<target){l=mid+1;}else{r=mid-1;}}return -1;}
}

1.2移除元素

class Solution {//双指针算法public int removeElement(int[] nums, int val) {int i=0;//标记目前位置 for(int j=0;j<nums.length;j++){if(nums[j]!=val){nums[i]=nums[j];i++;}}return i;}
}

1.3 有序数组的平方

class Solution {public int[] sortedSquares(int[] nums) {int n=nums.length;int[] ans=new int[n];int k=n-1;int i=0,j=nums.length-1;//类似于归并排序while(i<=j){if(nums[i]*nums[i]<nums[j]*nums[j]){ans[k--]=nums[j]*nums[j];j--;}else{ans[k--]=nums[i]*nums[i];i++;}}return ans;}
}

1.4长度最小的子数组

class Solution {public int minSubArrayLen(int target, int[] nums) {int minlen=0x3f3f3f3f;int sum=0;int j=0;for(int i=0;i<nums.length;i++){sum+=nums[i];while(sum>=target){//缩小区间minlen=Math.min(minlen,i-j+1);sum-=nums[j];j++;//   }}if(minlen==0x3f3f3f3f)return 0;return minlen;}
}

1.5螺旋矩阵II

class Solution {static boolean[][] st;public int[][] generateMatrix(int n) {st=new boolean[n][n];int[] dx={0,1,0,-1},dy={1,0,-1,0};int[][] ans=new int[n][n];int x=0,y=0,d=0;//横，纵坐标，转向指针for(int i=1;i<=n*n;i++){ans[x][y]=i;st[x][y]=true;int a=x+dx[d],b=y+dy[d];if(a<0 || a>=n || b<0 || b>=n || st[a][b]){d=(d+1)%4;a=x+dx[d];b=y+dy[d];}x=a;y=b;}return ans;}
}

2. 链表部分

2.1移除链表元素

/*** Definition for singly-linked list.* public class ListNode {*     int val;*     ListNode next;*     ListNode() {}*     ListNode(int val) { this.val = val; }*     ListNode(int val, ListNode next) { this.val = val; this.next = next; }* }*/
class Solution {public ListNode removeElements(ListNode head, int val) {if(head==null)return null;ListNode dummy=new ListNode(-1);dummy.next=head;ListNode cur=dummy;while(cur.next!=null){if(cur.next.val==val){cur.next=cur.next.next;}else cur=cur.next;}return dummy.next;}
}

2.2设计链表

2.3反转链表

/*** Definition for singly-linked list.* public class ListNode {*     int val;*     ListNode next;*     ListNode() {}*     ListNode(int val) { this.val = val; }*     ListNode(int val, ListNode next) { this.val = val; this.next = next; }* }*/
class Solution {public ListNode reverseList(ListNode head) {ListNode pre=null;ListNode cur=head;while(cur!=null){ListNode next=cur.next;cur.next=pre;pre=cur;cur=next;}return pre;}
}

2.4两两交换相邻的节点

/*** Definition for singly-linked list.* public class ListNode {*     int val;*     ListNode next;*     ListNode() {}*     ListNode(int val) { this.val = val; }*     ListNode(int val, ListNode next) { this.val = val; this.next = next; }* }*/
class Solution {public ListNode swapPairs(ListNode head) {ListNode dummy=new ListNode(-1);dummy.next=head;ListNode cur=dummy;while(cur.next!=null && cur.next.next!=null){ListNode a=cur.next;ListNode b=cur.next.next;cur.next=b;a.next=b.next;b.next=a;cur=a;}return dummy.next;}
}

2.5删除链表的倒数第n个节点

/*** Definition for singly-linked list.* public class ListNode {*     int val;*     ListNode next;*     ListNode() {}*     ListNode(int val) { this.val = val; }*     ListNode(int val, ListNode next) { this.val = val; this.next = next; }* }*/
class Solution {public ListNode removeNthFromEnd(ListNode head, int n) {ListNode dummy=new ListNode(-1);dummy.next=head;ListNode cur=head;int cnt=0;while(cur!=null){cnt++;cur=cur.next;}cur=dummy;cnt=cnt-n;while(cnt-->0)cur=cur.next;cur.next=cur.next.next;return dummy.next;}
}

2.6环形链表II

/*** Definition for singly-linked list.* class ListNode {*     int val;*     ListNode next;*     ListNode(int x) {*         val = x;*         next = null;*     }* }*/
public class Solution {public ListNode detectCycle(ListNode head) {ListNode slow=hasCycle(head);if(slow==null)return null;else{ListNode fast=head;while(fast!=slow){fast=fast.next;slow=slow.next;}}return slow;}public static ListNode hasCycle(ListNode head){ListNode slow=head;ListNode fast=head;while(fast!=null && fast.next!=null){fast=fast.next.next;slow=slow.next;if(fast==slow)return slow;}return null;}
}

2.7链表相交

/*** Definition for singly-linked list.* public class ListNode {*     int val;*     ListNode next;*     ListNode(int x) {*         val = x;*         next = null;*     }* }*/
public class Solution {public ListNode getIntersectionNode(ListNode headA, ListNode headB) {if(headA==null || headB==null)return null;int lenA=len(headA);int lenB=len(headB);ListNode curA=headA;ListNode curB=headB;if(lenA>lenB){int t=lenA-lenB;for(int i=0;i<t;i++){curA=curA.next;}while(curA!=null && curA!=curB){curA=curA.next;curB=curB.next;}return curA;}else{int t=lenB-lenA;for(int i=0;i<t;i++){curB=curB.next;}while(curA!=null && curA!=curB){curA=curA.next;curB=curB.next;}return curA;} }public static int len(ListNode head){int cnt=0;ListNode cur=head;while(cur!=null){cnt++;cur=cur.next;}return cnt;}}

3.哈希表