Leetcode刷题 2020.7.15

本文主要是介绍Leetcode刷题 2020.7.15，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

两数之和

这道题中的next指针的安排是重点。

/*** 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 *h = l1, *p = l1;while(l1 || l2){if(!l1)p -> next = new ListNode(0), l1 = p -> next;//此行处理为重点！！！if(!l2)l2 = new ListNode(0);l1 -> val += l2 -> val;if(l1 -> val > 9){if(l1 -> next)l1 -> next -> val ++;else l1 -> next = new ListNode(1);l1 -> val %= 10;} p = l1;     //注意保留之前的结点，防止之后的结点为空l1 = l1 -> next, l2 = l2 -> next;}return h;}
};

无重复的最长子串
运行错误的代码！！！

class Solution {
public:int lengthOfLongestSubstring(string s) {vector<int> ve(27, -1);int len = s.size(), t, Max = 0, k = 0;for (int i = 0; i < len; i++){t = s[i] - 'a';if(ve[t] == -1) ve[t] = i;else {Max = max(Max, i - k);for (int j = k; j < ve[t]; j++) ve[s[j] - 'a'] = -1;k = ve[t] + 1;ve[t] = i;}}if(!k) Max = len;return Max;}};

正解，滑动窗口！！！！！！！

class Solution {
public:int lengthOfLongestSubstring(string s) {unordered_map<char, int> tab;int len = s.size(), Max = 0, j = 0;for (int i = 0; i < len; i++){while(!tab.count(s[j]) && j < len) tab[s[j]] = 1, j++;if(j < len) tab.erase(s[i]);Max = max(Max, j - i);}return Max;}};

代码简化！！！！

class Solution {
public:int lengthOfLongestSubstring(string s) {unordered_map<char, int> tab; int len = s.size(), Max = 0;for (int i = 0, j = 0; j < len; j++){tab[s[j]]++;while(tab[s[j]] > 1) tab[s[i++]]--;Max = max(Max, j - i + 1);}return Max;}};

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