Google Interview Question for SDE1s

Country: United States

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A spare vector is a 1-D array / list which has a very high number of 0s or unimportant elements.

Thus, to build a SparseVector and implement the 4 methods, we can use a HashMap of a type <Integer, Integer>, where the key is the index of that element in the original list (which also includes the 0s), and the value is the actual value of that element.

To implement


, we simply return the value in the HashMap by using index as key.

To implement

increment(index, delta)

, we update the value in the HashMap by getting the already stored value at that index.

To implement


, we return the size of the HashMap.

To implement

dotProduct(Vector other)

, we iterate over the List of Map.Entry of the first HashMap, and for each key in the first HashMap that has a non-zero element in the other vector, we multiply the value of that key with the value of the element in the other vector, and add it to a sum. Finally, return sum.

- deejay November 05, 2017 | Flag Reply

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