g(a,b)=b(a+b−1)g(a−1,b−1)+(a−1)g(a−2,b+1)g(a,b)=b(a+b−1)g(a−1,b−1)+(a−1)g(a−2,b+1)g(a,b)=b(a+b−1)g(a−1,b−1)+(a−1)g(a−2,b+1) g(a,b)=a(a+b−1)g(a−1,b−1)+(b−1)g(a+1,b−2)g(a,b)=a(a+b−1)g(a−1,b−1)+(b−1)g(a+1,b−2)g(a,b)=a(a+b−1)g(a−1,b−1)+(b−1)g(a+1,b−2) 这两个式子。
官解里也说的很简略，看不懂/dk
