力扣算法经典第一题——两数之和（Java两种方式实现）

public static int[] twoSum1(int[] nums,int target) {
    for (int i = 0; i < nums.length; i++) {
        for (int j = i + 1; j < nums.length; j++) {
            if (nums[i] + nums[j] == target) {
                return new int[]{i, j};
            }
        }
    }
    return null;
}
public static void main(String[] args) {
    int nums[] = {2,4,6,7};
    int target = 10;
    int[] ints = twoSum1(nums, target);
    for (int i = 0;i < ints.length; i++){
        System.out.println(ints[i]);
    }
}

public int[] twoSum2(int[] nums, int target) {
    Map<Integer, Integer> map = new HashMap<>();

    for (int i = 0; i < nums.length; i++) {
        int result = target - nums[i];
        if (map.containsKey(result)) {
            return new int[] { map.get(result), i };
        }
        map.put(nums[i], i);
    }
    return new int[]{};
}

public static void main(String[] args) {
    int nums[] = {2,4,6,7};
    int target = 6;
    int[] ints = twoSum2(nums, target);
    for (int i = 0;i < ints.length; i++){
        System.out.println(ints[i]);
    }
}