安徽农业大学第一届编程与思维比赛试题

第一题思路：
排序，找到第一个a[i]>=i的位置i

public class Solutions {
    public static int solve(String[] args) {
        Scanner scanner = new Scanner( System.in );
        int n = scanner.nextInt();
        Integer[] a = new Integer[n];

        for( int i = 0; i < n; i++ )
            a[i] = scanner.nextInt();

        //从小到大排序
        Arrays.sort(a, new Comparator<Integer>() {
            @Override
            public int compare(Integer o1, Integer o2) {
                return o1 < o2 ? 1 : -1;
            }
        });

        int result = -1;
        for( int i = 0; i < n; i++ ){
            if( a[i] <= i ){
                result = i;
                break;
            }
        }
        return result == -1 ? n : result;
    }
}

第二题思路：
直接计算

public class Solutions {
    public static void main(String[] args) {
        Scanner scanner = new Scanner( System.in );
        int m = scanner.nextInt();
        int n = scanner.nextInt();
        double[][] a = new double[m][n], b = new double[m][n];

        for( int i = 0; i < m; i++ ){
            for( int j = 0; j < n; j++ ){
                a[i][j] = scanner.nextDouble();
            }
        }
        for( int i = 0; i < m; i++ ){
            for( int j = 0; j < n; j++ ){
                b[i][j] = scanner.nextDouble();
            }
        }

        double mse = 0;
        Double[] ab = new Double[ m * n ];
        for( int i = 0; i < m; i++ ){
            for( int j = 0; j < n; j++ ){
                double tmp = ( a[i][j] - b[i][j] ) * ( a[i][j] - b[i][j] );
                mse += tmp;
                ab[ i * m + j ] = tmp;
            }
        }

        //从大到小排序
        Arrays.sort( ab, new Comparator<Double>() {
            @Override
            public int compare(Double o1, Double o2) {
                return o1 < o2 ? 1 : -1;
            }
        });

        for( int i = 0; i < m * n / 10; i++ )
            mse -= ab[i];

        mse /= m * n - m * n / 10;
        System.out.printf( "%.5f", mse );
    }
}

第三题思路：
感染者和未感染者相遇，两个人掉头的效果和不掉头直行的效果是相同的，发挥想象力这个地方。

public class Solutions {
    public static void main(String[] args) {
        Scanner scanner = new Scanner( System.in );
        int m = scanner.nextInt();
        int[] a = new int[m];
        for( int i = 0; i < m; i++ )
            a[i] = scanner.nextInt();

        int res = 0;
        if( a[0] > 0 ){
            //正面而来的人全部感染
            for( int i = 1; i < m; i++ ){
                if( a[i] < 0 && ( - a[i] ) > a[0] )
                    res++;
            }
            //确实有正面而来的人
            if( res != 0 ){
                for( int i = 1; i < m; i++ ){
                    if( a[i] > 0 && a[i] > a[0] )
                        res++;
                }
            }
        }
        else if( a[0] < 0 ){
            for( int i = 0; i < m; i++ ){
                if( a[i] > 0 && a[i] < ( - a[0] ) )
                    res++;
            }

            if( res != 0 ){
                for( int i = 0; i < m; i++ ){
                    if( a[i] < 0 && ( - a[i] ) > ( - a[0] ) )
                        res++;
                }
            }
        }
        res += 1; //加上自己
        System.out.println( res );
    }
}

最后一个：
使用枚举，注意及时终止错误的枚举

import java.util.Scanner;
public class Solutions {
    public static void main(String[] args) {
        int res = 0;
        for( int i = 1; i <= 198 / 4; i++ ){
            for( int j = i; j + i <= 198 / 2; j++){
                for( int k = j; i + j + k <= 198 * 3 / 4; k++){
                    int m = 198 - i - j - k;
                    if( m >= k){
                        res++;
                        System.out.println( i + "," + j + "," + k + "," + m );
                    }
                }
            }
        }
        System.out.println( res );
    }
}