题目大意是求用k步从(1,1)走到(n,n)的方案数。
很简单的递推，用f[k,i,j]表示第k步走到(i,j)的方案数，则很明显f[k,i,j]=f[k-1,i-1,j]+f[k-1,i,j+1]+f[k-1,i+1,j]+f[k-1,i,j-1]，即统计k-1步时走到其周围四个格子的方案数。这题非常恶心的是要用高精度，极限数据超过了64位整形的范围，而如果用实型会因为浮点数运算产生误差（极度无语，都是整数加法运算）。
3026265 2008-08-07 11:51:46 Accepted 1536 FPC 00:00.01 432K IwfWcf@LZOI
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