Description:
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
9
//NKW 甲级真题1025
#pragma warning(disable:4996)
#include <stdio.h>
#include <stdlib.h>
#include <algorithm>
using namespace std;
const int maxn = 100010;
int a1[maxn];
int main(){
int n, left = 0, num;
scanf("%d", &n);
for (int i = 0; i < n; i++){
scanf("%d", &num);
a1[num] = i; //num的位置为i
if (num != i&&num != 0)
left++; //num非0,并且不在对应的位置上
}
int k = 1, cnt = 0;
while (left > 0){
if (a1[0] == 0){
while (k < n){
if (a1[k] != k){
swap(a1[0], a1[k]);
cnt++;
break;
}
k++; //很关键,
}
}
while (a1[0] != 0){
swap(a1[0], a1[a1[0]]);
cnt++;
left--;
}
}
printf("%d\n", cnt);
system("pause");
return 0;
}