根据此图,有
[1+ (I-1)]*(I-1)/2 ＜ A(I,J) ≤ [1+ I]*I/2
代入A(I,J) = 2009解得I = 63
J = 2009 - [1+ (I-1)]*(I-1)/2 = 56
即A(63,56) = 2009.
I = 63
J = 56
I + J = 63 + 56 = 119
此答案应是对的,我猜测书上给的答案是I = 63,J = 55,差一个数是因为书上算的“第XX”个有问题.
你可把A(4,2)代入我的方法算一下就知道了.
I = 4,J = 2
则[1+(I-1)](I-1)/2 = (1 + 3) *3/2 = 6
J = A(I,J) - 6 = 8 - 6 = 2
没错吧.