找出数组中和为S的一对组合，找出一组就行

考察点：数组

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