UVA 11925 Generating Permutations

构造法吧，类似冒泡排序，当队首是n的时候特判不换前两个位置了。

#include <iostream>
#include <algorithm>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <list>
#include <vector>
using namespace std;
const int INF = 0x7fffffff;
const int maxn = 300+5;
int n, a[maxn];

bool is() {
    for(int i = 0; i < n; ++i)
        if(a[i] != i+1) return false;
    return true;
}

void change() {
    int t = a[n-1];
    for(int i = n - 1; i >= 0; --i)
        a[i] = a[i-1];
    a[0] = t;
}

int main() {
    while(scanf("%d", &n) != EOF && n) {
        vector<int> ans;
        for(int i = 0; i < n; ++i)
            scanf("%d", &a[i]);
        while(!is()) {
            if(a[0] != n && a[0] > a[1]) {
                swap(a[0], a[1]);
                ans.push_back(1);
            }
            if(is()) break;
            change();
            ans.push_back(2);
        }
        for(int i = ans.size() - 1; i >= 0; --i)
            printf("%d", ans[i]);
        printf("\n");
    }
    return 0;
}