Leetcode刷题记录

刚刚开始刷LeetCode很多不明白的地方，写个博客记录一下心力路程

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].

暴力解法，不是很熟悉没有IDE的写法

class Solution {public:    vector<int> twoSum(vector<int>& nums, int target) {        vector<int> output;        for(int i=0;i<nums.size();i++)        {            for(int j=i+1;j<nums.size();j++)            {                if(nums[i]+nums[j]==target)                {                    output.push_back(i);                    output.push_back(j);                    return output;                }            }        }    }};

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.

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)Output: 7 -> 0 -> 8

对链表熟悉度还不够

/** * 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) {        ListNode head(0);        ListNode *preNode=&head;        int add=0;               ListNode *b1=l1,*b2=l2;        while(b1!=NULL||b2!=NULL||add>0)        {            ListNode *node=new ListNode(0);            int val1=b1?b1->val:0;            int val2=b2?b2->val:0;            b1=b1?b1->next:NULL;            b2=b2?b2->next:NULL;            node->val=(val1+val2+add)%10;            add=(val1+val2+add)/10;            preNode->next=node;            preNode=node;        }        return head.next;    }};

3. Longest Substring Without Repeating Characters

Given a string, find the length of the longest substring without repeating characters.Examples:Given "abcabcbb", the answer is "abc", which the length is 3.Given "bbbbb", the answer is "b", with the length of 1.Given "pwwkew", 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.

这个题还是蛮有难度的，因为不存在重复的字符，那么就当有重复的时候，计算两个重复的距离，如果没有重复的那么就一直减去-1

class Solution {public:    int lengthOfLongestSubstring(string s) {        vector<int> hash(256, -1);        int maxLen=0;        int start=-1;        for(int i=0;i<s.length();i++)        {            if(hash[s[i]]>start)            {                start=hash[s[i]];            }            hash[s[i]]=i;            maxLen=max(maxLen,i-start);        }        return maxLen;    }};