题目链接:https://pintia.cn/problem-sets/994805342720868352/problems/994805403651522560
题目描述
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.
输入
Each input file contains one test case, which gives a positive N (≤10^5 ) followed by a permutation sequence of {0, 1, …, N−1}. All the numbers in a line are separated by a space.
输出
For each case, simply print in a line the minimum number of swaps need to sort the given permutation.
样例输入
10
3 5 7 2 6 4 9 0 8 1
样例输出
9
代码
#include <cstdio>
#include <algorithm>
using namespace std;
const int maxn = 100010;
int pos[maxn];
int main() {
int n, ans = 0;
scanf("%d", &n);
int left = n - 1, num;
for(int i = 0; i < n; i++) {
scanf("%d", &num);
pos[num] = i;
if(num == i && num != 0) {
left--;
}
}
int k = 1;
while(left > 0) {
if(pos[0] == 0) {
while(k < n) {
if(pos[k] != k) {
swap(pos[0], pos[k]);
ans++;
break;
}
k++;
}
}
while(pos[0] != 0) {
swap(pos[0], pos[pos[0]]);
ans++;
left--;
}
}
printf("%d\n", ans);
return 0;
}