1.两数之和

class Solution {
    public int[] twoSum(int[] nums, int target) {
        HashMap<Integer,Integer> map = new HashMap();
        int[] res = new int[2];
        for(int i=0;i<nums.length;i++){
            if(i==0){
                map.put(nums[i],0);
            }else{
                if(map.containsKey(target-nums[i])){
                    res[0] = map.get(target - nums[i]);
                    res[1] = i;
                    return res;
                }else{
                    map.put(nums[i],i);
                }
            }
        }
        return null;
    }
}

遇到此类数组问题，可以多考虑一下map结构