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

get(index)

, 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

numNonZeros()

, 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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