Sum 系列题解 Two Sum题解 题目来源:https://leetcode.com/problems/two-sum/description/ Description 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 sol…

Combination Sum 系列题解 题目来源:https://leetcode.com/problems/combination-sum/description/ Description Given a set of candidate numbers (C) (without duplicates) and a target number (T), find all unique combinations in C where the candidate numbers sums to…

LeetCode--single-number系列 Question 1 Given an array of integers, every element appears twice except for one. Find that single one. Note: Your algorithm should have a linear runtime complexity. Could you implement it without using extra memory? Soluti…

Leetcode算法系列(链表)之两数相加 难度:中等给出两个 非空 的链表用来表示两个非负的整数.其中,它们各自的位数是按照 逆序 的方式存储的,并且它们的每个节点只能存储 一位 数字.如果,我们将这两个数相加起来,则会返回一个新的链表来表示它们的和.您可以假设除了数字 0 之外,这两个数都不会以 0 开头.示例:输入:(2 -> 4 -> 3) + (5 -> 6 -> 4)输出:7 -> 0 -> 8原因:342 + 465 = 807 链接:https://le…

LeetCode--Sum of Two Integers Question Calculate the sum of two integers a and b, but you are not allowed to use the operator + and -. Example: Given a = 1 and b = 2, return 3. Solution 异或操作有累加的效果,但是没有进位的效果.什么时候进位呢? 同时为1的时候进位,往前进一位,所以用交集操作,再移位,表示进位.…

Leetcode算法系列(链表)之删除链表倒数第N个节点 难度:中等给定一个链表,删除链表的倒数第 n 个节点,并且返回链表的头结点.示例:给定一个链表: 1->2->3->4->5, 和 n = 2.当删除了倒数第二个节点后,链表变为 1->2->3->5.说明:给定的 n 保证是有效的.链接:https://leetcode-cn.com/problems/remove-nth-node-from-end-of-list Python实现 # Definiti…

39. Combination Sum 1.Problem Find all possible combinations of k numbers that add up to a number n, given that only numbers from 1 to 9 can be used and each combination should be a unique set of numbers. Example 1: Input: k = 3, n = 7 Output: [[1,2,…

第一题是Two Sum 同样是用哈希表来做,需要注意的是在查打gap是要排除本身.比如target为4,有一个值为2,gap同样为2. vector<int> twoSum(vector<int> &num, int target) { unordered_map<int, int> mapping; vector<int> result; ; i < num.size(); i++) mapping[num[i]] = i; ; i <…

1.二叉树路径求指定和,需要注意的是由于有负数,所以即使发现大于目标值也不能返回false,而且返回true的条件有两个,到叶节点且等于sum,缺一不可 public boolean hasPathSum(TreeNode root, int sum) { if (root==null) return false; if (root.val==sum&&root.left==null&&root.right==null) return true; else return h…

Find the sum of all left leaves in a given binary tree. Example: 3 / \ 9 20 / \ 15 7 There are two left leaves in the binary tree, with values 9 and 15 respectively. Return 24. 这道题让我们求一棵二叉树的所有左子叶的和,那么看到这道题我们知道这肯定是考二叉树的遍历问题,那么最简洁的写法肯定是用递归,由于我们只需要累加左子叶…