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 );
}
}
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