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Combination Sum

Combination Sum (Python)

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Stack in Java

Stack using LL Stack using ArrayList Push At Bottom (Question)

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Recursion – Permutations

Permutation of String Permutation of Array

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Return ArrayList

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Sudoku Solver

Suduko Solver (Java) Suduko Solver (Python)

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N-Queens Solved

N-Queens (LeetCode)

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Maze Problems

We observe that left = r-1, c and right = c, r-1. For counting the total ways just return left + right. Including all paths (Using Backtracking) Output

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How Many Numbers Are Smaller Than the Current Number

1365. How Many Numbers Are Smaller Than the Current Number (Easy) Given the array nums, for each nums[i] find out how many numbers in the array are smaller than it. That is, for each nums[i] you have to count the number of valid j’s such that j != i and nums[j] < nums[i]. Return the answer in an array. Example 1: Input: nums = [8,1,2,2,3] Output: … Read more

Number of Good Pairs (LeetCode)

1512. Number of Good Pairs (Easy) Given an array of integers nums, return the number of good pairs. A pair (i, j) is called good if nums[i] == nums[j] and i < j. Example 1: Input: nums = [1,2,3,1,1,3] Output: 4 Explanation: There are 4 good pairs (0,3), (0,4), (3,4), (2,5) 0-indexed. Example 2: Input: nums = [1,1,1,1] Output: 6 Explanation: Each pair in the array are good. … Read more