4. The goal of the 4-queens problem is to place 4 queens on a 4 rows 4 columns chessboard, such that no two queens attach each other. One solution to the 4 queens problem is shown in Figure 3. Please design a search based solution to solve the 4-queens problem. Your solution must include following four components a. Define state [0.5 pt] b. Define successor function [0.5 pt c. Show state graph [0.5 pt] d. Show how to find solutions from state graph [0.5 pt] Q1 Q2 Q3 egi Figure 3