494. Target Sum You are given an integer array nums and an integer target. You want to build an expression out of nums by adding one of the symbols ‘+’ and ‘-’ before each integer in nums and then concatenate all the integers. For example, if nums = [2, 1], you can add a ‘+’ before 2 and a ‘-’ before 1 and concatenate them to build the expression “+2-1”. Return the number of different expressions that you can build, which evaluates to target. ...
93. Restore IP Addresses Given a string s containing only digits, return all possible valid IP addresses that can be obtained from s. You can return them in any order. A valid IP address consists of exactly four integers, each integer is between 0 and 255, separated by single dots and cannot have leading zeros. For example, “0.1.2.201” and “192.168.1.1” are valid IP addresses and “0.011.255.245”, “192.168.1.312” and “192.168@1.1” are invalid IP addresses. ...
139. Word Break Given a string s and a dictionary of strings wordDict, return true if s can be segmented into a space-separated sequence of one or more dictionary words. Note that the same word in the dictionary may be reused multiple times in the segmentation. Example 1: Input: s = "leetcode", wordDict = ["leet","code"] Output: true Explanation: Return true because "leetcode" can be segmented as "leet code". Example 2: Input: s = "applepenapple", wordDict = ["apple","pen"] Output: true Explanation: Return true because "applepenapple" can be segmented as "apple pen apple". Note that you are allowed to reuse a dictionary word. Example 3: Input: s = "catsandog", wordDict = ["cats","dog","sand","and","cat"] Output: false Constraints: ...
322. Coin Change You are given an integer array coins representing coins of different denominations and an integer amount representing a total amount of money. Return the fewest number of coins that you need to make up that amount. If that amount of money cannot be made up by any combination of the coins, return -1. You may assume that you have an infinite number of each kind of coin. ...
328. Odd Even Linked List Given the head of a singly linked list, group all the nodes with odd indices together followed by the nodes with even indices, and return the reordered list. The first node is considered odd, and the second node is even, and so on. Note that the relative order inside both the even and odd groups should remain as it was in the input. Example 1: Input: head = [1,2,3,4,5] Output: [1,3,5,2,4] ...
91. Decode Ways A message containing letters from A-Z can be encoded into numbers using the following mapping: ‘A’ -> “1” ‘B’ -> “2” … ‘Z’ -> “26” To decode an encoded message, all the digits must be grouped then mapped back into letters using the reverse of the mapping above (there may be multiple ways). For example, “11106” can be mapped into: “AAJF” with the grouping (1 1 10 6) “KJF” with the grouping (11 10 6) Note that the grouping (1 11 06) is invalid because “06” cannot be mapped into ‘F’ since “6” is different from “06”. ...
276. Paint Fence You are painting a fence of n posts with k different colors. You must paint the posts following these rules: Every post must be painted exactly one color. At most one pair of adjacent fence posts can have the same color. Given the two integers n and k, return the number of ways you can paint the fence. Example 1: Input: n = 3, k = 2 Output: 6 Explanation: All the possibilities are shown. Note that painting all the posts red or all the posts green is invalid because there can only be at most one pair of adjacent posts that are the same color. Example 2: Input: n = 1, k = 1 Output: 1 Example 3: Input: n = 7, k = 2 Output: 42 ...
63. Unique Paths II A robot is located at the top-left corner of a m x n grid (marked ‘Start’ in the diagram below). The robot can only move either down or right at any point in time. The robot is trying to reach the bottom-right corner of the grid (marked ‘Finish’ in the diagram below). Now consider if some obstacles are added to the grids. How many unique paths would there be? ...
64. Minimum Path Sum Given a m x n grid filled with non-negative numbers, find a path from top left to bottom right, which minimizes the sum of all numbers along its path. Note: You can only move either down or right at any point in time. Example 1: Input: grid = [[1,3,1],[1,5,1],[4,2,1]] Output: 7 Explanation: Because the path 1 → 3 → 1 → 1 → 1 minimizes the sum. ...
1859. Sorting the Sentence A sentence is a list of words that are separated by a single space with no leading or trailing spaces. Each word consists of lowercase and uppercase English letters. A sentence can be shuffled by appending the 1-indexed word position to each word then rearranging the words in the sentence. For example, the sentence “This is a sentence” can be shuffled as “sentence4 a3 is2 This1” or “is2 sentence4 This1 a3”. Given a shuffled sentence s containing no more than 9 words, reconstruct and return the original sentence. ...