Shortest path and 2nd shortest path using Dijkstra – code

shortest path using Dijkstra java

What is Dijkstra’s algorithm? Dijkstra’s algorithm is an algorithm to find the shortest paths between vertices in a graph. It uses greedy technique by picking the un-visited vertex with the lowest distance. When all vertices have been evaluated, the result is the shortest path. Find 2nd shortest path is a …

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Build hierarchy tree – Code

build hierarchy tree listing

Build hierarchy tree reads employee data and build a corporation hierarchy tree from the list. HashMap plays important role to store the data when reading the input. The trick of this question is to find the root. You can get the root by finding the employee without the manager. Starting …

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Shortest path from source to destination in matrix – Code

shortest path in matrix

Shortest path in matrix is to find the shortest distance from the the source to the destination. As you know, graph can be represented as adjacent matrix. Therefore, we can use the Breadth First Search algorithm in graph to solve this problem. BFS starts from the source node. It explores …

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Autocomplete with trie (3 solutions) – Code

autocomplete with trie listing

Autocomplete is a feature that search box returns the suggestions based on what you have typed. Autocomplete with trie provides an implementation of auto-complete by using data structure trie. A trie is a tree-like data structure in which every node stores a character. After building the trie, strings or substrings …

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Prefix to postfix (2 solutions) – stack and recursion

Prefix To Postfix

In mathematics expressions, there are infix, prefix and postfix notations. Infix notation is characterized by the placement of operators between operands. For example, the plus sign in 2 + 2. Prefix notation is a notation in which operators precede their operands, such as + 3 4. Postfix notation is a …

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Word break using memoization – Code

wordbreak with memoization

Word break is to divide a string into sub-strings that defined in dictionary. The problem is usually solved with recursion. The time complexity is exponential. Here we introduce word break using memoization, which helps to improve complexity. Memoization is one of Dynamic programming(DP) techniques. DP is able to solve a …

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Word ladder using bi-directional BFS – time complexity explained

word ladder bidirectional bfs

Word ladder is to find the number of steps to convert one string to another by changing one letter at a time. The intermediate words should be valid and can be found in pre-defined dictionary. The intuitive solution is using breadth first search (BFS). It starts from the original word, …

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Depth first search in matrix using recursion

DFS and adjacent matrix

An adjacency matrix is a 2d array representing a graph. The nodes are the headings for the rows and columns. The element in the cell indicates whether an edge is present between two nodes. Depth first search (DFS) is an algorithm used to traverse or search in a graph. The …

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Find K closest points to origin (3 solutions) – time complexity explained

K closest points

The K closest problem is to find K closest points to the pointer(0,0) (it is called center or origin). The input k is to specify how many points you should return. The Euclidean distance formula is √[ (x2–x1)^2 + (y2–y1)^2]. For this question, we don’t need to calculate the actual …

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Huffman coding and decoding – Step by step

huffman coding

Huffman coding is an algorithm to generate the binary code based on the frequencies of corresponding characters in the input string. By applying it, we compress the input string by using the generated code. We can also use the code to decompress to get the original string. Here are the …

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