力扣labuladong——一刷day18

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前言

双指针技巧处理数组问题，常用的是左右指针，和快慢指针

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一、力扣26. 删除有序数组中的重复项

class Solution {
    public int removeDuplicates(int[] nums) {
        int i, j;
        for(i = 0,j = 0; j < nums.length;){
            if(nums[i] == nums[j]){
                j ++;
            }else{
                nums[++i] = nums[j++];
            }
        }
        return i + 1;
    }
}

二、力扣83. 删除排序链表中的重复元素

/**
 * 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 deleteDuplicates(ListNode head) {
        if(head == null)return null;
        ListNode pre = head, p = head;
        while(p != null){
            if(p.val == pre.val){
                p = p.next;
            }else{
                pre.next = p;
                pre = pre.next;
                p = p.next;
            }
        }
        pre.next = null;
        return head;
    }
}

三、力扣27. 移除元素

class Solution {
    public int removeElement(int[] nums, int val) {
        if(nums.length == 0){
            return 0;
        }
        int i , j;
        for(i = 0, j = 0; j < nums.length;){
            if(nums[j] == val){
                j ++;
            }else{
                nums[i++] = nums[j++];
            }
        }
        return i;
    }
}

四、力扣283. 移动零

class Solution {
    public void moveZeroes(int[] nums) {
        for(int i = 0,j = 0; j < nums.length;){
            if(nums[j] == 0){
                j ++;
            }else{
                int temp = nums[i];
                nums[i] = nums[j];
                nums[j] = temp;
                i ++;
                j ++;
            }
        }
    }
}

五、力扣167. 两数之和 II - 输入有序数组

class Solution {
    public int[] twoSum(int[] numbers, int target) {
        int[] res = new int[2];
        for(int left = 0, right = numbers.length-1; left < right;){
            int cur = numbers[left] + numbers[right];
            System.out.println(cur);
            if(cur > target){
                right --;
            }else if(cur < target){
                left ++;
            }else{
                res[0] = left+1;
                res[1] = right+1;
                break;
            }
        }
        return res;
    }
}

六、力扣344. 反转字符串

class Solution {
    public void reverseString(char[] s) {
        for(int i = 0, j = s.length-1; i < j; i ++,j--){
            char temp = s[i];
            s[i] = s[j];
            s[j] = temp;
        }
    }
}

七、力扣最长回文子串

class Solution {
    String res;
    int count = 1;
    public String longestPalindrome(String s) {
        res = s.substring(0,1);
        for(int i = 0; i <s.length(); i ++){
            fun(s,i,i);
            if(i + 1 < s.length()){
                fun(s,i , i + 1);
            }
        }
        return res;
    }
    public void fun(String s, int left, int right){
        while(left >=0 && right < s.length()){
            if(s.charAt(left) == s.charAt(right)){
                left --;
                right ++;
            }else{
                break;
            }
        }
        left ++;
        right --;
        if((right - left + 1) > count){
            count = right - left + 1;
            res = s.substring(left,right+1);
        }
    }
}