10-排序6 Sort with Swap(0, i)

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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 1

Sample Output:

9

 code

# include <cstdio>int data[100010];
bool visited[100010];int travCircle(int s)
{int current = data[s];int cnt = 1;visited[s] = true;while (current != s){visited[current] = true;cnt++;current = data[current];}return cnt;
}int main(void)
{int n;scanf("%d", &n);for (int i = 0; i < n; ++i) visited[i] = false;for (int i = 0; i < n; ++i) scanf("%d", &data[i]);int ans = 0;for (int i = 0; i < n; ++i){if (visited[i]) continue;int tmp = travCircle(i);if (i == 0){if (tmp == 1) ans += 0;else ans += (tmp - 1);}else{if (tmp == 1) ans += 0;else ans += (tmp + 1);}}printf("%d\n", ans);return 0;
}