First, connect all adjacent numbers together to form a 5*5 grid array. * * * has 40 line segments. Each line segment has a value. Each value represents the total number of two endpoints that change together from beginning to end. 1 in the upper left corner is connected by two lines. Since 1 has not changed, the sum of the two lines is 0. Look at three 3s, two of which are wired, and the 3 of 1 has four lines. The sum of these three groups of lines (three, three and four) is -2 (because three is more than the last 65438. Then look at five fives ... The reason why I don't look at 2 and 4 is because each line segment is not added repeatedly, at least once. It is concluded that the sum of all the last line segments is 0* 1+2*3+4*4+(5-A)+3*6+8, which should be equal to the difference between the sum of the following elements and the sum of the above elements, and then divided by 2 (because the total number of a line segment pair has changed by 2). The equation can be listed as 0 * 1+2 * 3+4 * 4. Get A=5.