DAY1_leetcode

 1 class Solution {
 2     public int[] twoSum(int[] nums, int target) {
 3         Map<Integer, Integer> map = new HashMap<>();
 4         for(int i = 0; i<nums.length;i++){
 5             int tmp = target - nums[i];
 6             if(map.containsKey(tmp)){
 7                 return new int[]{map.get(tmp),i};   //存在即返回
 8             }
 9             map.put(nums[i],i);  //不存在，则加入
10         }
11         throw new IllegalArgumentException("No two sum solution");
12     }
13 }

 1 class Solution {
 2     public int reverse(int x) {
 3         try{
 4             if(x>0){
 5                 StringBuilder str = new StringBuilder().append(x);
 6                 return Integer.parseInt(str.reverse().toString());
 7             }else{
 8                 StringBuilder str = new StringBuilder().append(-x);
 9                 return Integer.parseInt(str.reverse().toString())*(-1);
10             }
11         }catch(NumberFormatException e){
12             return 0;
13 
14         }
15     }
16 }