个人记录-LeetCode 1.Two Sum

问题： Given an array of integers, return indices of the two numbers such that they add up to a specific target.

You may assume that each input would have exactly one solution.

代码示例： 1、暴力解法

public class Solution { public int[] twoSum(int[] nums, int target) { if(nums == null || nums.length < 2) { return null; } for(int i = 0; i < nums.length - 1; ++i) { for (int j = i + 1; j < nums.length; ++j) { if (nums[i] + nums[j] == target) { return new int[] {i, j}; } } } return null; } }

2、利用hashMap来快速查找

public int[] twoSum(int[] nums, int target) { Map<Integer, Integer> map = new HashMap<>(); for (int i = 0; i < nums.length; i++) { //求出需要的匹配数字 int complement = target - nums[i]; //判断匹配数字是否已经加入到map中 //更快，而且可以避免加入重复数字时HashMap的替换 if (map.containsKey(complement)) { return new int[] { map.get(complement), i }; } map.put(nums[i], i); } throw new IllegalArgumentException("No two sum solution"); }