LeetCode1. Two Sum

题目：

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.

Example:

Given nums = [2, 7, 11, 15], target = 9,

Because nums[0] + nums[1] = 2 + 7 = 9,
return [0, 1].


我的解决方法，弱爆了但是还是要贴出来：

package Mine;

public class TwoSum01 {
    public int[] twoSum(int[] nums, int target) {
        int[] result = new int[2];
        int length = nums.length;
        
        for (int i = 0; i < length ; i ++){
            for (int j = i+1 ; j < length ; j ++) {
                if(nums[i] + nums[j] == target) {
                    result[0] = i;
                    result[1] = j;
                }
            }
        }
        return result;
    }
}

别人家孩子：

package BOOK;

import java.util.HashMap;
import java.util.Map;

public class TwoSum01 {
    public int[] twoSum(int[] nums, int target) {
        Map<Integer, Integer> map = new HashMap<>();
        for(int i = 0; i < nums.length; i ++) {
            int x = nums[i];
            if(map.containsKey(target - x)) {
                return new int[] {map.get(target -x) , i};
            }
            map.put(x, i);
        }
        throw new IllegalArgumentException("No two sum solution");
    }
}