```
/**
* Create a new hash map to store the value and corresponding index in origin array
* Search the result of target number minus current number in the hasp map
* If another number is existed in hash map, return the index of two numbers
* Otherwise, put current number as key and index as value to the hasp map
* <p>
* After traverse all array, then return null, means no such sum of two numbers in given array
*
* @param nums a set of numbers
* @param target sum value to be searched
* @return index of two numbers
*/
public int[] twoSum(int[] nums, int target) {
Map<Integer, Integer> valueMap = new HashMap<>();
for (int index = 0; index < nums.length; index++) {
int anotherNum = target - nums[index];
if (valueMap.containsKey(anotherNum)) {
return new int[]{valueMap.get(anotherNum), index};
}
valueMap.put(nums[index], index);
}
return null;
}
```

reference: https://github.com/xinerd/algorithm/blob/master/LeetCode/src/cn/fmachine/leetcode/easy/TwoSum.java