1. Two Sum
Given an array of integers, return indices of the two numbers such that they add up to a specific target. You may assume that each input would have exactly one solution, and you may not use the same element twice. Example: Given nums = [2, 7, 11, 15], target = 9, Because nums[0] + nums[1] = 2 + 7 = 9, return [0, 1].
class Solution { public: vector<int> twoSum(vector<int>& nums, int target) { unordered_map<int, int> num_index_dict; vector<int> res; for (int i = 0; i < nums.size(); i++) { if (num_index_dict.find(nums[i]) != num_index_dict.end()) { int index = num_index_dict[nums[i]]; res.push_back(index); res.push_back(i); return res; } else { num_index_dict[target - nums[i]] = i; } } return res; } };
2. Add Two Numbers
You are given two non-empty linked lists representing two non-negative integers. The digits are stored in reverse order and each of their nodes contain a single digit. Add the two numbers and return it as a linked list. You may assume the two numbers do not contain any leading zero, except the number 0 itself. Example: Input: (2 -> 4 -> 3) + (5 -> 6 -> 4) Output: 7 -> 0 -> 8 Explanation: 342 + 465 = 807.
/** * Definition for singly-linked list. * struct ListNode { * int val; * ListNode *next; * ListNode(int x) : val(x), next(NULL) {} * }; */ class Solution { public: ListNode* addTwoNumbers(ListNode* l1, ListNode* l2) { int carry = 0; ListNode* dummy_head = new ListNode(0); ListNode* head = dummy_head; while (l1 || l2 || carry) { int temp = carry; if (l1) { temp += l1 -> val; l1 = l1 -> next; } if (l2) { temp += l2 -> val; l2 = l2 -> next; } carry = temp / 10; int cur_val = temp % 10; head -> next = new ListNode(cur_val); head = head -> next; } return dummy_head -> next; } };
3. Longest Substring Without Repeating Characters
Given a string, find the length of the longest substring without repeating characters. Example 1: Input: "abcabcbb" Output: 3 Explanation: The answer is "abc", with the length of 3. Example 2: Input: "bbbbb" Output: 1 Explanation: The answer is "b", with the length of 1. Example 3: Input: "pwwkew" Output: 3 Explanation: The answer is "wke", with the length of 3. Note that the answer must be a substring, "pwke" is a subsequence and not a substring.
class Solution { public: int lengthOfLongestSubstring(string s) { if (s.empty()) { return 0; } int left = 0; int right = 0; int pos_dict[128]; for (int i = 0; i < 128; i++) { pos_dict[i] = -1; } int res = 0; while (right < s.size()) { char cur_char = s[right]; if (pos_dict[(int)cur_char] == -1) { pos_dict[(int)cur_char] = right; right += 1; } else { res = max(res, right - left); int last_index = pos_dict[(int)cur_char]; // 注意此处 for (int i = left; i<= last_index; i++) { pos_dict[(int)s[i]] = -1; } left = last_index + 1; pos_dict[(int)cur_char] = right; right += 1; } } res = max(res, right - left); return res; } };