Create N_Queens_1

The algorithm I designed is following such steps, based on recursion: 
1) First, one arraylist-config-is applied to store the configuration of each "place-search" step. The 0th element config stores the position of queen in 0th row, i.e. if config.get(0) is 2, then there is one queen at the 2nd column, 0th row. 
2) Secondly, I search for all reasonable answers, or configurations at in a for loop. Because we can know that for the 0th row, each position(from 0 to n - 1) might lead to a reasonable configuration.
3) Thirdly, recursively search. The function will find the reasonable position for next row, and continue until the config.size() is n, which means now it has found one good configuration, then it can be added to result.