LeetCode.82.15(双指针)

82.删除排序链表中的重复元素-ii

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */

class Solution {
  public:
    ListNode *deleteDuplicates(ListNode *head) {
        if (!head || !head->next)
            return head;
        ListNode *front = head->next;
        ListNode *behind = new ListNode(0, head);
        int temp = head->val;
        head = behind;
        while (front) {
            if (front->val == temp) {
                if (behind->next->val != temp) {
                    behind = behind->next;
                }
                behind->next = front->next;
                front = front->next;
            } else {
                temp = front->val;
                front = front->next;
                if (front && temp != front->val)
                    behind = behind->next;
            }
        }
        return head->next;
        // 166/166 cases passed (4 ms)
        // Your runtime beats 93.62 % of cpp submissions
        // Your memory usage beats 93.04 % of cpp submissions (10.7 MB)
    }
};

15.三数之和

class Solution {
  public:
    vector<vector<int>> threeSum(vector<int> &nums) {
        if (nums.size() < 3)
            return {};
        sort(nums.begin(), nums.end());
        vector<vector<int>> ans;
        for (int i = 0; i < nums.size() - 2;) {
            int left = i + 1, right = nums.size() - 1;
            while (left < right) {
                if (nums[i] + nums[left] + nums[right] > 0) {
                    right--;
                } else if (nums[i] + nums[left] + nums[right] < 0) {
                    left++;
                } else {
                    ans.push_back({nums[i], nums[left], nums[right]});
                    int temp = nums[left];
                    while (left < right && temp == nums[left])
                        left++;
                }
            }
            int temp = nums[i];
            while (i < nums.size() - 2 && temp == nums[i])
                i++;
        }
        return ans;
        // 318/318 cases passed (72 ms)
        // Your runtime beats 73.27 % of cpp submissions
        // Your memory usage beats 94.2 % of cpp submissions (19.3 MB)
    }
};