算法

(双指针) $O(n)$

利用双指针的做法。 不断移动左指针，调整右指针的位置，直到相等即可。

C++ 代码

class Solution {
public:
    vector<int> twoSum(vector<int>& nums, int target) {
        int l = 0;
        int r = nums.size() -1;
        while(l < r){
            if(nums[l] + nums[r] == target){
                vector<int> indexs{l+1,r+1};
                return indexs;
            } else if(nums[l] + nums[r] > target){
                r--;
            } else{
                l++;
            }
        }
        return vector<int>();
    }
};

Java 代码

class Solution {
    public int[] twoSum(int[] numbers, int target) {
        int left = 0;
        int right = numbers.length - 1;

        while (left < right) {
            if (numbers[left] + numbers[right] == target) {
                return new int[] {left + 1, right + 1};
            }
            else if (numbers[left] + numbers[right] < target) {
                left++;
            }
            else right--;
        }

        return new int[0];
    }
}

Python 代码

class Solution:
    def twoSum(self, numbers: List[int], target: int) -> List[int]:
        l, r = 0, len(numbers) - 1
        while l < r:
            value = numbers[l] + numbers[r]
            if value == target:
                return [l + 1, r + 1]
            elif value < target:
                l += 1
            else: r -= 1
        return []