Facebook Interview Question for Software Engineers

Country: United States
Interview Type: Phone Interview

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Get the longest arithmetic progression:

public static int[] llac(int[] array) {
        if(array.length == 0) return new int[]{};
        int maxLen = 1, //len of longest sequence
            end = array[0], //end number of sequence
            step = 0;
        Map<Integer,Map<Integer, Integer>> index_to_llac = new HashMap<>(); //Map<currentIndex, Map<difference, length>>

        for(int current = 1; current < array.length; current++) {
            index_to_llac.put(current, new HashMap<>());
            for(int prev = 0; prev < current; prev++) {
                int diff = array[current] - array[prev];
                int length = 2;
                if(index_to_llac.containsKey(prev) && index_to_llac.get(prev).containsKey(diff)) {
                    length = index_to_llac.get(prev).get(diff) + 1;
                Map<Integer, Integer> diff_to_llac = index_to_llac.get(current);
                //if this is a arithmetic progression with [diff] exists before current, add 1 to the length to include current in the progression
                //otherwise, [prev, current] forms a progression of size 2
                diff_to_llac.put(diff, length);

                if(maxLen < length) {
                    maxLen = length;
                    end = array[current];
                    step = diff;

        int[] sequence = new int[maxLen];
        for(int i = maxLen - 1; i >= 0; i--) {
            sequence[i] = end;
            end -= step;
        return sequence;

- aonecoding November 03, 2017 | Flag Reply

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