Is it possible to use a hash map to monitor progress while looping through this array in JavaScript?

Question

Is it possible to use a hash map to monitor progress while looping through this array in JavaScript?

I've been exploring some algorithmic problems and I'm puzzled about the most efficient way to solve this particular question. While nested for loops are an option, they don't seem like the optimal choice. I'm considering using a hash map to keep track of the temperature and the index associated with it.

Imagine you have a list of daily temperatures. Your task is to create a new list that indicates, for each day in the input, how many days you would need to wait until a warmer temperature occurs. If there's no future day with a higher temperature, mark 0 instead. For instance, if the input list is temperatures = [73, 74, 75, 71, 69, 72, 76, 73], then your output should look like this: [1, 1, 4, 2, 1, 1, 0, 0].

javascript algorithm

Answer 1

Answer №1

There are a variety of techniques that can be employed for this particular problem. While @PlatypusMaximus suggests an approach that works when iterating from the end, you can also tackle it by moving forward through the array, which may offer a clearer understanding:

As you traverse the array, maintain a list of indexes where the 'closest following warmer day' has not yet been determined. This list starts off empty.
For each element, eliminate any indexes from the list with lower temperatures and assign their 'closest following warmer day' to the current index.
By the time you reach the end, any remaining indexes in the list do not have a 'closest following warmer day' and are assigned 0s.

The key part is: Each time you add an element to the list, all previous elements are either equal or higher in temperature. Consequently, the index list stays sorted in decreasing order of temperature. In step (2), this means that only the elements at the tail end of the list (possibly implemented as a stack) need consideration rather than searching through the entire list, resulting in an efficient O(N) time complexity for the process.

Answer 2

There are a variety of techniques that can be employed for this particular problem. While @PlatypusMaximus suggests an approach that works when iterating from the end, you can also tackle it by moving forward through the array, which may offer a clearer understanding:

As you traverse the array, maintain a list of indexes where the 'closest following warmer day' has not yet been determined. This list starts off empty.
For each element, eliminate any indexes from the list with lower temperatures and assign their 'closest following warmer day' to the current index.
By the time you reach the end, any remaining indexes in the list do not have a 'closest following warmer day' and are assigned 0s.

The key part is: Each time you add an element to the list, all previous elements are either equal or higher in temperature. Consequently, the index list stays sorted in decreasing order of temperature. In step (2), this means that only the elements at the tail end of the list (possibly implemented as a stack) need consideration rather than searching through the entire list, resulting in an efficient O(N) time complexity for the process.

Answer 3

Answer №2

One approach is to fill the result array with zeroes and then iterate through the given values by utilizing an object to store key-value pairs of indices and temperatures.

If a value is encountered that is higher than the current temperature in the temporary object, the difference between the indices is calculated and assigned at the corresponding index while removing the key from the object.

The temperatures are assigned as keys in the object along with their respective indices.

var data = [73, 74, 75, 71, 69, 72, 76, 73],
    //     [ 1,  1,  4,  2,  1,  1,  0,  0]
    result = Array.from(data, _ => 0);

data.reduce((tempObj, tempVal, index) => 
    tempObj.filter(([storedTemp, storedIndex]) => {
        if (storedTemp >= tempVal) return true;
        result[storedIndex] = index - storedIndex;
    }).concat([[tempVal, index]]),
    []
);

console.log(result);

Answer 4

One approach is to fill the result array with zeroes and then iterate through the given values by utilizing an object to store key-value pairs of indices and temperatures.

If a value is encountered that is higher than the current temperature in the temporary object, the difference between the indices is calculated and assigned at the corresponding index while removing the key from the object.

The temperatures are assigned as keys in the object along with their respective indices.

var data = [73, 74, 75, 71, 69, 72, 76, 73],
    //     [ 1,  1,  4,  2,  1,  1,  0,  0]
    result = Array.from(data, _ => 0);

data.reduce((tempObj, tempVal, index) => 
    tempObj.filter(([storedTemp, storedIndex]) => {
        if (storedTemp >= tempVal) return true;
        result[storedIndex] = index - storedIndex;
    }).concat([[tempVal, index]]),
    []
);

console.log(result);

Is it possible to use a hash map to monitor progress while looping through this array in JavaScript?

Answer №1

Answer №2

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