Given a binary tree and a sum, determine if the tree has a root-to-leaf path such that adding up all the values along the path equals the given sum. For example:Given the below binary tree and sum = 22, 5 / \ 4 8 / / \ 11 13 4 / \ \ 7 2 1 return true…

题目在这里: https://leetcode.com/problems/two-sum/ [标签]Array; Hash Table [个人分析] 这个题目,我感觉也可以算是空间换时间的例子.如果是O(n^2)的那种思路,就是对于一个数字,去扫剩下的所有数字,看有没有能够加起来和为target的组合.但是如果加入一个哈希表,我们扫过的数字都可以记录下来. 我用的是 (target - number) 作为key, 用number在nums中的 index 作为 value, 遇到一个新的数字n…

Given a set of candidate numbers (C) and a target number (T), find all unique combinations in C where the candidate numbers sums to T. The same repeated number may be chosen from C unlimited number of times. Note: All numbers (including target) will…

注意点: HashMap<Integer, Integer> return new int[]{}; 3 2 4 target:6 return null; public int[] twoSum(int[] nums, int target) { HashMap<Integer, Integer> m = new HashMap<>(); for(int i = 0; i < nums.length; ++i){ if(m.containsKey(target…

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. Ensure that numbers within the set are sorted in ascending order. Example 1…

题目: 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. 翻译: 给定一组整数,两个数字的返回索引,它们的和会等于一个特定…

题目: 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. 翻译: 给定一组整数,两个数字的返回索引,它们的和会等于一个特定…

题目难度:Medium 题目: Given an array S of n integers, are there elements a, b, c, and d in S such that a + b + c + d = target? Find all unique quadruplets in the array which gives the sum of target. Note: The solution set must not contain duplicate quadrup…

LeetCode one Two Sum (JAVA) 简介:给定一个数组和目标值,寻找数组中符合求和条件的两个数. 问题详解: 给定一个数据类型为int的数组,一个数据类型为int的目标值target,要求是在数组中寻求两个数字,使得两个数求和的值等于给定的target,要求以数组返回符合条件的索引. 技巧:可以假设数组中没有重复元素,因为我们只返回一个符合条件的数组,所以数组中只需要一个符合要求的数字就可以了. 举例: 给定数组 nums={5,8,7,2,11},target= 10, 因…

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]…

Given a collection of candidate numbers (candidates) and a target number (target), find all unique combinations in candidates where the candidate numbers sums to target. Each number in candidates may only be used once in the combination. Note: All nu…

Given a binary tree and a sum, determine if the tree has a root-to-leaf path such that adding up all the values along the path equals the given sum. For example:Given the below binary tree and sum = 22, 5 / \ 4 8 / / \ 11 13 4 / \ \ 7 2 1 return true…

Given a binary tree and a sum, find all root-to-leaf paths where each path's sum equals the given sum. For example:Given the below binary tree and sum = 22, 5 / \ 4 8 / / \ 11 13 4 / \ / \ 7 2 5 1 return [ [5,4,11,2], [5,8,4,5] ] 112. Path Sum 的拓展,上一…

Given an array of integers that is already sorted in ascending order, find two numbers such that they add up to a specific target number. The function twoSum should return indices of the two numbers such that they add up to the target, where index1 m…

Design and implement a TwoSum class. It should support the following operations:add and find. add - Add the number to an internal data structure.find - Find if there exists any pair of numbers which sum is equal to the value. For example,add(1); add(…

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: [[1,2,4]] Example 2: Input: k = 3, n…

Given an integer array nums, find the sum of the elements between indices i and j (i ≤ j), inclusive. Example: Given nums = [-2, 0, 3, -5, 2, -1] sumRange(0, 2) -> 1 sumRange(2, 5) -> -1 sumRange(0, 5) -> -3 Note: You may assume that the array do…

Given a 2D matrix matrix, find the sum of the elements inside the rectangle defined by its upper left corner (row1, col1) and lower right corner (row2, col2). The above rectangle (with the red border) is defined by (row1, col1) = (2, 1) and (row2, co…

Given an integer array with all positive numbers and no duplicates, find the number of possible combinations that add up to a positive integer target. Example: nums = [1, 2, 3] target = 4 The possible combination ways are: (1, 1, 1, 1) (1, 1, 2) (1,…

Given a Binary Search Tree and a target number, return true if there exist two elements in the BST such that their sum is equal to the given target. Example 1: Input: 5 / \ 3 6 / \ \ 2 4 7 Target = 9 Output: TrueExample 2: Input: 5 / \ 3 6 / \ \ 2 4…

LeetCode 1 Two Sum 解题报告 偶然间听见leetcode这个平台,这里面题量也不是很多200多题,打算平时有空在研究生期间就刷完,跟跟多的练习算法的人进行交流思想,一定的ACM算法积累可以对以后在对算法中优化带来好处.Ok,今天是我做的第一题Add Two Sum. 题目要求 Given an array of integers, find two numbers such that they add up to a specific target number. The fu…

题目: Given an array of integers that is already sorted in ascending order, find two numbers such that they add up to a specific target number. The function twoSum should return indices of the two numbers such that they add up to the target, where inde…

一. 题目 1. Two Sum II Given an array of integers that is already sorted in ascending order, find two numbers such that they add up to a specific target number. The function twoSum should return indices of the two numbers such that they add up to the ta…

一. 题目 1. Two SumTotal Accepted: 241484 Total Submissions: 1005339 Difficulty: Easy 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 solutio…

leetcode - 40. Combination Sum II - Medium descrition Given a collection of candidate numbers (C) and a target number (T), find all unique combinations in C where the candidate numbers sums to T. Each number in C may only be used once in the combinat…

leetcode - 39. Combination Sum - Medium descrition 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 T. The same repeated number may be chosen from…

Given a collection of candidate numbers (candidates) and a target number (target), find all unique combinations in candidates where the candidate numbers sums to target. Each number in candidates may only be used once in the combination. Note: All nu…

You are given a binary tree in which each node contains an integer value. Find the number of paths that sum to a given value. The path does not need to start or end at the root or a leaf, but it must go downwards (traveling only from parent nodes to…

题目:求所有全排列 难度:Medium 题目内容: Given a collection of distinct integers, return all possible permutations. 翻译:给定一组各不相同的整数,返回所有可能的排列. Example: Input: [1,2,3] Output: [ [1,2,3], [1,3,2], [2,1,3], [2,3,1], [3,1,2], [3,2,1] ] 我的思路:每种情况中,每一个元素只出现一次,只是之间的顺序不同,那么…

You are given a binary tree in which each node contains an integer value. Find the number of paths that sum to a given value. The path does not need to start or end at the root or a leaf, but it must go downwards (traveling only from parent nodes to…