LeetCode1---两数之和

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

/**
 *功能描述 :两数之和
 * @author lkr
 * @date 2019/3/5
 */
public class Solution1 {
    //暴力法
    public static int[] twoSum(int[] nums, int target) {
        int[] arr = new int[2];
        for(int i=0;i<nums.length;i++){
            for(int j=i+1;j<nums.length;j++){
                int sum = nums[i] + nums[j];
                if(target == sum){
                    arr[0] = i;
                    arr[1] = j;
                }
            }
        }
        return arr;
    }

    //一遍哈希表
    public static int [] oneHashtable(int[] nums,int target){
        Map<Integer,Integer> map = new HashMap();
        for (int i=0;i<nums.length;i++){
            int value = target - nums[i];
            if(map.containsKey(value)){
                /*int[] arr = {map.get(value),i};
                return arr;*/
                return new int[] {map.get(value),i};//为什么map.get(value)在前面？
            }
            map.put(nums[i],i);
        }
        throw new IllegalArgumentException("NO TWO SUM SOLUTION");
    }

    public static void main(String[] args){
        int [] nums = {2,7,11,15,9};
        int target = 20;
        //int [] arr = twoSum(nums,target);
        int [] arr = oneHashtable(nums,target);
        System.out.println(Arrays.toString(arr));
    }
}