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Given any permutation of the numbers {0, 1, 2,..., N-1}, it is easy to sort them in increasing order. But what if Swap(0, *) is the ONLY operation that is allowed to use? For example, to sort {4, 0, 2, 1, 3} we may apply the swap operations in the following way:
Swap(0, 1) => {4, 1, 2, 0, 3}
Swap(0, 3) => {4, 1, 2, 3, 0}
Swap(0, 4) => {0, 1, 2, 3, 4}
Now you are asked to find the minimum number of swaps need to sort the given permutation of the first N nonnegative integers.
Input Specification:
Each input file contains one test case, which gives a positive N (<=105) followed by a permutation sequence of {0, 1, ..., N-1}. All the numbers in a line are separated by a space.
Output Specification:
For each case, simply print in a line the minimum number of swaps need to sort the given permutation.
Sample Input:10 3 5 7 2 6 4 9 0 8 1Sample Output:
9
1 #include <iostream> 2 #include <set> 3 4 using namespace std; 5 6 set<int> WrongIndex; 7 int sequence[100000]; 8 9 int main() 10 { 11 int n; 12 cin >> n; 13 for (int i = 0; i < n; i++) 14 { 15 int num; 16 cin >> num; 17 sequence[i] = num; 18 if (num != i) 19 WrongIndex.insert(i); 20 } 21 int totalNum = WrongIndex.size(); 22 int cycle = 0; 23 while (!WrongIndex.empty()) 24 { 25 int initial = *(WrongIndex.begin()); 26 int next = sequence[initial]; 27 WrongIndex.erase(initial); 28 while (next != initial) 29 { 30 WrongIndex.erase(next); 31 next = sequence[next]; 32 } 33 cycle++; 34 } 35 if (totalNum == 0) 36 cout << 0; 37 else if (sequence[0] != 0) 38 cout << totalNum + cycle - 2; 39 else 40 cout << totalNum + cycle; 41 }
PAT 1067. Sort with Swap(0,*) (25)
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原文地址：http://www.cnblogs.com/jackwang822/p/4730719.html
