st表里面的 f[i][j]=max(f[i][j−1],f[i+(1<<(j−1))][j−1])f[i][j]=max(f[i][j-1],f[i+(1<<(j-1))][j-1])f[i][j]=max(f[i][j−1],f[i+(1<<(j−1))][j−1])是怎么来的？如何理解？
