根據(jù)此圖,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
此答案應(yīng)是對(duì)的,我猜測(cè)書(shū)上給的答案是I = 63,J = 55,差一個(gè)數(shù)是因?yàn)闀?shū)上算的“第XX”個(gè)有問(wèn)題.
你可把A(4,2)代入我的方法算一下就知道了.
I = 4,J = 2
則[1+(I-1)](I-1)/2 = (1 + 3) *3/2 = 6
J = A(I,J) - 6 = 8 - 6 = 2
沒(méi)錯(cuò)吧.