C#•9mo ago

❔ How do I check for an array key in Dictionary?

Dictionary<int[], int> test =
    new()
    {
        { new int[] { 2, 3 }, 3 }, // <- this one
        { new int[] { 3, 3 }, 6 },
        { new int[] { 3, 2 }, 3 }
    };

Console.WriteLine(test.ContainsKey(new int[] { 2, 3 }));

Dictionary<int[], int> test =
    new()
    {
        { new int[] { 2, 3 }, 3 }, // <- this one
        { new int[] { 3, 3 }, 6 },
        { new int[] { 3, 2 }, 3 }
    };

Console.WriteLine(test.ContainsKey(new int[] { 2, 3 }));

output:

False

11 Replies

TheRanger•9mo ago

yeah you need to create a class that implements IEqualityComparer and do the logic to make it equal if the elements are the same and inject an instance of that class to the Dictionary's constructor or perhaps there is a built in class that already does that

MODiX•9mo ago

TheRanger

REPL Result: Success

class IntArrayComparer : IEqualityComparer<int[]>
{
    public bool Equals(int[] array, int[] other)
    {

        return array.SequenceEqual(other);
    }

    public int GetHashCode(int[] array)
    {
       return array.Length;
    }
}

// your code
Dictionary<int[], int> test =
    new(new IntArrayComparer())
    {
        { new int[] { 2, 3 }, 3 }, // <- this one
        { new int[] { 3, 3 }, 6 },
        { new int[] { 3, 2 }, 3 }
    };

Console.WriteLine(test.ContainsKey(new int[] { 2, 3 }));
Console.WriteLine(test.ContainsKey(new int[] { 2, 4 }));
Console.WriteLine(test.ContainsKey(new int[] { 2, 4, 3 }));
Console.WriteLine(test.ContainsKey(new int[] { 3, 3 }));
Console.WriteLine(test.ContainsKey(new int[] { 3, 2 }));

class IntArrayComparer : IEqualityComparer<int[]>
{
    public bool Equals(int[] array, int[] other)
    {

        return array.SequenceEqual(other);
    }

    public int GetHashCode(int[] array)
    {
       return array.Length;
    }
}

// your code
Dictionary<int[], int> test =
    new(new IntArrayComparer())
    {
        { new int[] { 2, 3 }, 3 }, // <- this one
        { new int[] { 3, 3 }, 6 },
        { new int[] { 3, 2 }, 3 }
    };

Console.WriteLine(test.ContainsKey(new int[] { 2, 3 }));
Console.WriteLine(test.ContainsKey(new int[] { 2, 4 }));
Console.WriteLine(test.ContainsKey(new int[] { 2, 4, 3 }));
Console.WriteLine(test.ContainsKey(new int[] { 3, 3 }));
Console.WriteLine(test.ContainsKey(new int[] { 3, 2 }));

Console Output

True
False
False
True
True

True
False
False
True
True

Compile: 781.850ms | Execution: 120.559ms | React with ❌ to remove this embed.

TheRanger•9mo ago

or you can make the class contain a generic argument

MODiX•9mo ago

TheRanger

REPL Result: Success

class ArrayComparer<T> : IEqualityComparer<T[]>
{
    public bool Equals(T[] array, T[] other)
    {
        return array.SequenceEqual(other);
    }


    public int GetHashCode(T[] array)
    {
       return array.Length;
    }
}
//your code
Dictionary<int[], int> test =
    new(new ArrayComparer<int>())
    {
        { new int[] { 2, 3 }, 3 }, // <- this one
        { new int[] { 3, 3 }, 6 },
        { new int[] { 3, 2 }, 3 }
    };

Console.WriteLine(test.ContainsKey(new int[] { 2, 3 }));
Console.WriteLine(test.ContainsKey(new int[] { 2, 4 }));
Console.WriteLine(test.ContainsKey(new int[] { 2, 4, 3 }));
Console.WriteLine(test.ContainsKey(new int[] { 3, 3 }));
Console.WriteLine(test.ContainsKey(new int[] { 3, 2 }));

class ArrayComparer<T> : IEqualityComparer<T[]>
{
    public bool Equals(T[] array, T[] other)
    {
        return array.SequenceEqual(other);
    }


    public int GetHashCode(T[] array)
    {
       return array.Length;
    }
}
//your code
Dictionary<int[], int> test =
    new(new ArrayComparer<int>())
    {
        { new int[] { 2, 3 }, 3 }, // <- this one
        { new int[] { 3, 3 }, 6 },
        { new int[] { 3, 2 }, 3 }
    };

Console.WriteLine(test.ContainsKey(new int[] { 2, 3 }));
Console.WriteLine(test.ContainsKey(new int[] { 2, 4 }));
Console.WriteLine(test.ContainsKey(new int[] { 2, 4, 3 }));
Console.WriteLine(test.ContainsKey(new int[] { 3, 3 }));
Console.WriteLine(test.ContainsKey(new int[] { 3, 2 }));

Console Output

True
False
False
True
True

True
False
False
True
True

Compile: 754.357ms | Execution: 138.209ms | React with ❌ to remove this embed.

TheRanger•9mo ago

but the question is, why Dictionary<int[], int> ? if you will tell me what are you trying to achieve, i may provide a better solution

Jibz•9mo ago

i was trying this problem https://leetcode.com/problems/unique-paths/ and I wanted to solve this with DP so I wanted to store the grid as key and the result as value

LeetCode

Unique Paths - LeetCode

Can you solve this real interview question? Unique Paths - There is a robot on an m x n grid. The robot is initially located at the top-left corner (i.e., grid[0][0]). The robot tries to move to the bottom-right corner (i.e., grid[m - 1][n - 1]). The robot can only move either down or right at any point in time. Given the two integers m and n, ...

Jibz•9mo ago

but then, I kinda just converted to string and store it as <string, int> like key = string.Format()

exokem•9mo ago

What is the effect of storing the grid as the key? There is only ever one grid and I wouldn't expect any cell to have state your end goal is to determine the number of possible routes to get from a point A to a point B so you could try instead tracking the number of possible routes to get from A to each other point in the grid (the subproblem for a given cell is the number of routes from A to that cell) then your solution is the value assigned to the point B in this case you would only need one 2d array, or even a map with points as keys

jcotton42•9mo ago

As the arrays appear to be a fixed size, I would just use ValueTuple

Jibz•9mo ago

yeah that could work too. But using dictionary was just my first thought

Accord•9mo ago

Was this issue resolved? If so, run /close - otherwise I will mark this as stale and this post will be archived until there is new activity.

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❔ How do I check for an array key in Dictionary?