Interview Algorithms: Difference between revisions
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==Data Structures== | ==Data Structures== | ||
===Hashmap=== | ===Hashmap=== | ||
Also known as a dictionary or associative array. | Also known as a dictionary or associative array. These are used everywhere.<br> | ||
If you know your inputs are bounded non-negative values, then you can use an array like <code>std::vector</code>.<br> | |||
Otherwise, just use a hashmap to build a lookup table. | |||
===Segment Trees=== | ===Segment Trees=== | ||
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== | ==Dynamic Programming== | ||
DP is mostly used for Google interviews. Meta for example will not ask DP problems. You should study DP after everything else or if you've secured a Google interview. | |||
If you're given an arbitrary function with <code>n*m</code> possible inputs, you should aim to find an O(n*m) solution. | |||
==Prefix Sum== | |||
If you need to do a reduce operation on a continuous subarray, chances are you can turn that O(n) into O(1) by building a prefix sum. Similarly for 2D with axis-aligned regions. | |||
==Tricks== | |||
===Bit tricks=== | |||
See https://www.geeksforgeeks.org/bit-tricks-competitive-programming/ | |||
It's rare that you will need bit tricks for an interview. However some leetcode questions may require them to get decent performance. | |||
The most useful one is | |||
<pre> | |||
n & n-1 | |||
</pre> | |||
which zeros the least significant set bit. | |||
E.g. this can be used to count the number of set bits. | |||
===Bitmask=== | |||
===Counting=== | |||
Counting as in tabulate not as in combinatorial counting. | |||
====Finding duplicates in an array==== | ====Finding duplicates in an array==== | ||