Google Foobar Numbers Station

问题

Im trying to solve a google foobar challenge but I am stuck on how to change this to use recursion. any pointers would be helpful

public static int[] answer(int[] l, int t) {
    // convert the array into a list
    List<Integer> list = new ArrayList<>();
    for (int i : l) {
        list.add(i);
    }
    for (int i = 0; i < list.size(); i++) {
        Integer n = list.get(i);
        if (i >= 1) {
            Integer nMinus1 = list.get(i - 1);
            Integer nMinus2;
            Integer nMinus3;
            Integer nMinus4;
            Integer nMinus5;
            Integer nMinus6;
            if (n + nMinus1 == t) {
                // done
                return new int[]{i - 1, i};
            } else if (i >= 2) {
                nMinus2 = list.get(i - 2);
                if (n + nMinus1 + nMinus2 == t) {
                    // done
                    return new int[]{i - 2, i};
                } else if (i >= 3) {
                    nMinus3 = list.get(i - 3);
                    if (n + nMinus1 + nMinus2 + nMinus3 == t) {
                        // done
                        return new int[]{i - 3, i};
                    } else if (i >= 4) {
                        nMinus4 = list.get(i - 4);
                        if (n + nMinus1 + nMinus2 + nMinus3 + nMinus4 == t) {
                            // done
                            return new int[]{i - 4, i};
                        } else if (i >= 5) {
                            nMinus5 = list.get(i - 5);
                            if (n + nMinus1 + nMinus2 + nMinus3 + nMinus4 + nMinus5 == t) {
                                // done
                                return new int[]{i - 5, i};
                            } else if (i >= 6) {
                                nMinus6 = list.get(i - 6);
                                if (n + nMinus1 + nMinus2 + nMinus3 + nMinus4 + nMinus5 + nMinus6 == t) {
                                    // done
                                    return new int[]{i - 6, i};
                                }
                            }
                        }
                    }
                }
            }
        }
    }
    return new int[]{-1, -1};
}

Here is the question:

Given the list l as [4, 3, 5, 7, 8] and the key t as 12, the function answer(l, t) would return the list [0, 2] because the list l contains the sub-list [4, 3, 5] starting at index 0 and ending at index 2, for which 4 + 3 + 5 = 12, even though there is a shorter sequence that happens later in the list (5 + 7). On the other hand, given the list l as [1, 2, 3, 4] and the key t as 15, the function answer(l, t) would return [-1, -1] because there is no sub-list of list l that can be summed up to the given target value t = 15.

回答1:

You probably don't need an arraylist. You could perform a double loop on the array l. Why do you want recursion?

You could do something like:

public static int[] answer(int[] l, int t) {
    int[] rets = {-1, -1};
    int sum=0;
    for (int i=0; i<l.length; i++) {
        sum=0;
        for (int j=i; j<l.length; j++) {
            sum+=l[j];
            if (sum > t) break;
            if (sum == t) {
                rets[0] = i;
                rets[1] = j;
                return rets;
            }    
        }
    }
    return rets;
}

回答2:

Just submitted my solution.. it got accepted, so I know it was accepted by Google:

(I believe this will be slightly faster than above solution since it will break the loops and return if the target is greater than sum of all numbers in the array.)

public static int[] answer(int[] l, int t){
   int sum =0;
    List<Integer> indexes = new ArrayList<>();

    for(int j=0;j<l.length;j++){
        sum = 0;
        indexes.clear();
        for(int i=j;i<l.length;i++){

            sum += l[i];
            indexes.add(i);

            if(sum >= t){
                break;
            }

        }

        if(sum == t){
            break;
        }
        else if(sum > t){
            continue;
        }
        else{
            return new int[] {-1,-1};
        }

    }

    int[] returnArray = new int[2];

    if(indexes.size()>0){
        returnArray[0] = indexes.get(0);
        returnArray[1] = indexes.get(indexes.size()-1);
    }

    return returnArray;
}

来源：https://stackoverflow.com/questions/40695207/google-foobar-numbers-station