采用窮舉法的話(huà), 其時(shí)間復(fù)雜度為 O((n^2)/2). 略去窮舉法的實(shí)現(xiàn).

采用如下實(shí)現(xiàn), 其時(shí)間復(fù)雜度為 O(n), 空間復(fù)雜度增至 O(n).

public class Test {

    public static void main(String[] args) {
        int[] numberArr = {3, 5, 0, 35, 3, 25, 6, 3, 7, 6};
        int sum = 13;
        int[] result = find(numberArr, sum);
        System.out.println("滿(mǎn)足條件的兩個(gè)數(shù)的索引為: " + Arrays.toString(result));
    }

    public static int[] find(int[] numberArr, int sum) {
        Map<Integer, Integer> temp = new HashMap<>();

        for (int i = 0; i < numberArr.length; i++) {
            int number = numberArr[i];
            int target = sum - number;
            Integer targetIdx = temp.get(target);

            if (targetIdx != null) {
                return new int[]{targetIdx, i};
            } else {
                temp.put(number, i);
            }
        }

        return null;
    }
}