Discussion on: Finding the coordinates of an element in a 2D array

[Christian Engel]

Here is another approach when you want to go for SPEED (maybe you need to look up coordinates very often?).

let fastMap = null;

function computeFastMap(in2DArray){
    fastMap = {};

    for(let x = 0; x < in2dArray[0].length; x++){
        for(let y = 0; y < in2dArray.length; y++){
            fastMap[in2dArray[y][x]] = {x, y};
        }
    }
}

function find2DCoordinate(value){
    if(!fastMap){
        throw new Error("Compute the fastMap, first!");
    }

    return fastMap[value] || null;
}

To make this work, you need to call computeFastMap(grid) at the beginning, once.
Afterwards, you can call find2DCoordinate() often but since all coordinates are pre-computed, the lookup in the
map is basically "for free" and will be VERY fast.

[Karey Higuera]

Good call, I hadn't worked under the assumption of needing to do multiple lookups. It reminds me of a tweet I saw of using coordinate pairs in tuples for dictionary lookups in Python twitter.com/nedbat/status/15225434...