第一题：
public class Main {
public static void main(String[] args) { Scanner sc = new Scanner(System.in); long n = sc.nextInt(); long m = sc.nextInt(); long sum = n/2 * m; System.out.println(sum); }}
第二题：
import java.util.*;public class Main { public static void main(String[] args) { Scanner sc = new Scanner(System.in); int k = sc.nextInt(); int a = sc.nextInt(); int x = sc.nextInt(); int b = sc.nextInt(); int y = sc.nextInt(); int[][] dp = new int[x+y+1][k+1]; for (int i = 0; i < x+y+1; i++) dp[i][0] = 1; for (int i = 1; i < x+y+1; i++) { for (int j = 1; j <= k; j++) { if (i <= x) { if (j >= a) dp[i][j] = (dp[i-1][j] + dp[i-1][j-a]) % 1000000007; else dp[i][j] = dp[i-1][j] % 1000000007; } else if (i <= x+y) { if (j >= b) dp[i][j] = (dp[i-1][j] + dp[i-1][j-b]) % 1000000007; else dp[i][j] = dp[i-1][j] % 1000000007; } } } System.out.println(dp[x+y][k]); }
}
第三题：（我没时间了，所以没写出来，这个是从大神那Copy过来的）
import java.util.*;public class Main { static class Pair { int time; int level; public Pair(int time, int level) { this.time = time; this.level = level; } } public static void main(String[] args) { Scanner sc = new Scanner(System.in); int n = sc.nextInt(); int m = sc.nextInt(); Pair[] machine = new Pair[n]; Pair[] task = new Pair[m]; // input for (int i = 0; i < n; i++) machine[i] = new Pair(sc.nextInt(), sc.nextInt()); for (int i = 0; i < m; i++) task[i] = new Pair(sc.nextInt(), sc.nextInt()); int[] cnt = new int[105]; Comparator<Pair> comparator = (a, b) -> { if (a.time == b.time) return b.level - a.level; else return b.time - a.time; }; Arrays.sort(machine, comparator); Arrays.sort(task, comparator); long sum = 0; int j = 0, cnt1 = 0; for(int i = 0;i < m;i++) { while(j < n && machine[j].time >= task[i].time) { cnt[machine[j].level]++; j++; } for(int k = task[i].level; k < 101; k++) { if(cnt[k] != 0) { cnt[k]--; sum += 200*task[i].time + 3*task[i].level; cnt1++; break; } } } System.out.println(cnt1 + " " + sum); }
}
