题解 | #两数之和#

两种解题思路

1. 暴力双遍历比较

   import java.util.*;
   public class Solution {
    /**
     * 
     * @param numbers int整型一维数组 
     * @param target int整型 
     * @return int整型一维数组
     */
    public int[] twoSum (int[] numbers, int target) {
        // write code here
         int[] ans = new int[2];
         for(int index1 = 1; index1 <= numbers.length; index1++){
            for(int index2 = index1 + 1; index2 <= numbers.length; index2++){
                if(numbers[index1 - 1] + numbers[index2 - 1] == target){
                    ans[0] = index1;
                    ans[1] = index2;
                     return ans;
                }
           }
         }
        return null;
   
    }
   }

2. HashMap反向索引快速定位到index，一次遍历就结束了。

        Map<Integer, Integer> map = new HashMap();
        for(int i = 0; i < numbers.length; i++){
            if(map.get(target - numbers[i]) != null){
                return new int[]{map.get(target - numbers[i]) + 1, i + 1};
            }else{
                map.put(numbers[i], i);
            }
        }
        return new int[]{-1, -1};