Use the search below to find our solutions for selected questions!
Problem statement Given a list, nums, of distinct numbers, return all possible permutations. Sample input
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1 |
[1,2,3] |
Sample output
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1 2 3 4 5 6 7 8 |
[ [1,2,3], [1,3,2], [2,1,3], [2,3,1], [3,1,2], [3,2,1] ] |
Solution In another post we showed how this problem can be solved using a recursive technique by swapping. We stumbled upon a nice iterative solution that we thought might be worth . . . Read more
Problem statement Given a list, nums, of distinct numbers, return all possible permutations. Sample input
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1 |
[1,2,3] |
Sample output
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1 2 3 4 5 6 7 8 |
[ [1,2,3], [1,3,2], [2,1,3], [2,3,1], [3,1,2], [3,2,1] ] |
Solution We are using a technique called permutations by swapping. Full code
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 |
class Solution(object): def swap(self, nums, i, j): tmp = nums[i] nums[i] = nums[j] nums[j] = tmp def solve(self, nums, i, result): if i == len(nums)-1: result.append(list(nums)) return for j in range(i, len(nums)): self.swap(nums, i, j) self.solve(nums, i+1, result) self.swap(nums, i, j) def permute(self, nums): """ :type nums: List[int] :rtype: List[List[int]] """ ans = [] self.solve(nums, 0, ans) return ans def main(): solution = Solution() print(solution.permute([1,2,3])) if __name__ == "__main__": main() |
Problem statement You are given an 2D matrix / array representing an image. Rotate matrix by 90 degrees (clockwise) in-place. Solution We will work through the matrix layers. The layers of a matrix are illustrated below in different colours: There are a total of layers. We then iterate of the . . . Read more
Problem statement A time series is a series of data points indexed in time order. They are commonly used in the financial world, especially in stock markets. In this challenge you are working with a time series of stock prices. You are given historical records where the stock at time . . . Read more
Problem statement Given a string containing just the characters ( and ), find the length of the longest valid (well-formed) parentheses substring. Sample input
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1 |
(() |
Sample output
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1 |
2 |
Sample input 1
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1 |
)()()) |
Sample output 1
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1 |
4 |
Solution We will solve this problem using a Stack. We are going to iterate . . . Read more
Problem statement Given an array of integers sorted in ascending order, find the starting and ending position of a given target value. If the target is not found in the array, return . Sample input
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1 2 |
[5, 7, 7, 8, 8, 10] 8 |
Sample output
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1 |
[3, 4] |
Solution
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 |
class Solution(object): def search(self, nums, n, start, end, ans): if start > end: return mid = start + (end - start)//2 if n == nums[mid]: ans[0] = min(ans[0], mid) ans[1] = max(ans[1], mid) self.search(nums, n, start, mid-1, ans) self.search(nums, n, mid+1, end, ans) def searchRange(self, nums, target): """ :type nums: List[int] :type target: int :rtype: List[int] """ ans = [len(nums), -1] self.search(nums, target, 0, len(nums)-1, ans) if ans[0]==len(nums): return [-1,-1] return ans def main(): solution = Solution() print(solution.searchRange([5, 7, 7, 8, 8, 10], 8)) if __name__ == "__main__": main() |
Problem statement Given n non-negative integers representing an elevation map where the width of each bar is 1, compute how much water it is able to trap after raining. Sample input
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1 |
[6,8,5,0,0,6,5] |
Sample output
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1 |
13 |
Solution We can solve this problem in time by iterating over the array twice. Once . . . Read more
Problem statement Given a digit string, return all possible letter combinations that the number could represent. A mapping of digit to letters (just like on the telephone buttons) is given below. Sample input
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1 |
"23" |
Sample output
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1 |
["ad", "ae", "af", "bd", "be", "bf", "cd", "ce", "cf"] |
Solution
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 |
class Solution(object): def solve(self, digits, i, current, ans): """ :type digits: str :rtype: List[str] """ if len(digits) == 0: if len(current) > 0: ans.append(current) return mapping = {2:['a','b','c'], 3:['d','e','f'], 4:['g','h','i'], 5:['j','k','l'], 6:['m','n','o'], 7:['p','q','r', 's'], 8:['t','u','v'], 9:['w','x','y', 'z']} d = ord(digits[i]) - 48 chars = mapping[d] for c in chars: self.solve(digits[i+1:], i, current + c, ans) def letterCombinations(self, digits): """ :type digits: str :rtype: List[str] """ ans = [] self.solve(digits, 0, '', ans) return ans def main(): solution = Solution() print(solution.letterCombinations("23")) print(solution.letterCombinations("")) if __name__ == "__main__": main() |
Problem statement Suppose an array sorted in ascending order is rotated at some pivot unknown to you beforehand. (i.e., might become ). You are given a target value to search. If found in the array return its index, otherwise return . You may assume no duplicate exists in the array. . . . Read more
Problem statement The string PAYPALISHIRING is written in a zigzag pattern on a given number of rows like this:
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1 2 3 |
P A H N A P L S I I G Y I R |
And then read line by line: PAHNAPLSIIGYIR. Write the code that will take a string and make this conversion given a number of rows: Sample input
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1 2 |
"PAYPALISHIRING" 3 |
Sample output
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1 |
"PAHNAPLSIIGYIR" |
. . . Read more