2D - 2SUM 问题：
对于两个序列 {an},{bn}\{a_n\},\{b_n\}{an},{bn}，对于每个二元组 (x,y)(x,y)(x,y),求 F(x,y)=∑1≤i,j≤n[ai+aj=x][bi+bj=y]F(x,y)=\sum_{1\le i,j\le n}[a_i+a_j=x][b_i+b_j=y]F(x,y)=∑1≤i,j≤n[ai+aj=x][bi+bj=y] 值域 2×1032\times 10^32×103，n≤106n\le 10^6n≤106 .
