UVA 331 Mapping the Swaps

大意；求在最小的交换次数的情况下使得序列升序排列的方案数。

思路：冒泡排序对应最小交换数，然后回溯。

CODE：

#include <iostream>
#include <cstdlib>
#include <cstdio>
#include <cstring>
using namespace std;

int ans;
int n;
int a[1001];

int check(int *a)
{
    for(int i = 0; i < n-1; i++)
    {
        if(a[i] > a[i+1]) return 0;
    }
    return 1;
}

void swap(int &a, int &b)
{
    int t = a;
    a = b;
    b = t;
}

void dfs(int *a)
{
    if(check(a))
    {
        ans++;
        return ;
    }
    else for(int i = 0; i < n-1; i++)
    {
        if(a[i] > a[i+1])
        {
            swap(a[i], a[i+1]);
            dfs(a);
            swap(a[i], a[i+1]);
        }
    }
}

int main()
{
    int times = 0;
    while(~scanf("%d", &n) && n)
    {
        ans = 0;
        for(int i = 0; i < n; i++) scanf("%d", &a[i]);
        if(!check(a))
        {
            dfs(a);
        }
        printf("There are %d swap maps for input data set %d.\n", ans, ++times);
    }
    return 0;
}

转载于:https://www.cnblogs.com/g0feng/archive/2012/10/13/2722444.html

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