PAT 1067 Sort with Swap(0,*)

#include <cstdio>

#include <cstdlib>

#include <vector>



using namespace std;



int swap(vector<int> &numpos, int va, int vb) {

    //printf("swap(%d at %d, %d at %d)\n", va, numpos[va], vb, numpos[vb]);

    int pa = numpos[va];

    int pb = numpos[vb];

    numpos[va] = pb;

    numpos[vb] = pa;

}



int pick_first_mismatch_value(vector<int> &numpos, int start) {

    int i = start;

    int len = numpos.size();

    while (i < len) {

        if (numpos[i] != i) {

            return i;

        

        }

        i++;

    }

    return -1;

}



int main() {

    int N;

    scanf("%d", &N);

    

    vector<int> numpos(N);

    

    int value;

    for (int i=0; i<N; i++) {

        scanf("%d", &value);

        numpos[value] = i;

    }

    

    int step = 0;

    int b = 0;

    for (;;) {

        if (numpos[0] == 0) {

            b = pick_first_mismatch_value(numpos, b);

            if (b <= 0) {

                break;

            }

            swap(numpos, 0, b);

            step++;

            continue;

        }

        swap(numpos, 0, numpos[0]);



        step++;

    }

    

    printf("%d", step);

    

    return 0;

}