package com.q0001_two_sum;

import java.util.Arrays;

import java.util.HashMap;

import java.util.Map;

/**

* @author xjn

* @since 2020-02-15

* https://leetcode-cn.com/problems/two-sum/

* 1. 两数之和

*

* 时间复杂度O(n)

* 空间复杂度O(n)

*/

public class Solution {

public int[] twoSum(int[] nums, int target) {

if (nums == null || nums.length == 0) {

return null;

}

//k:value

//v:index

Map<Integer, Integer> map = new HashMap<>();

for (int i = 0; i < nums.length; i++) {

if (map.containsKey(target - nums[i])) {

return new int[]{i, map.get(target - nums[i])};

}

map.put(nums[i], i);

}

return null;

}

public static void main(String[] args) {

Solution solution = new Solution();

int[] ints = solution.twoSum(new int[]{2, 7, 11, 15}, 9);

System.out.println(Arrays.toString(ints));

}

}