Given a set A [1 ... n], and one from A to its own mapping f, to find the larges...

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给定一集合A[1...n]和一个从A 到其自身的映射f,寻找元素个数最多的一个子集S属于A，并使得S 满足： 1．f 把S 映射到自身； 2．S 中没有两个元素映射到相同的元素。-Given a set A [1 ... n], and one from A to its own mapping f, to find the largest number of elements in a subset of S belongs to A, and makes the S satisfy: 1. f to S is mapped to itself 2. No two elements of S mapped to the same element.