Codeforces Round #243 (Div. 2)

A。所有ai求和的值大於S，則輸出NO，其餘輸出YES

import java.io.PrintWriter;
import java.util.Arrays;
import java.util.Scanner;

public class Codeforces {

	public static void main(String[] args) {
		new TaskA().run();
	}
	
}

class TaskA {
	
	Scanner in = new Scanner(System.in);
	PrintWriter out = new PrintWriter(System.out);

	public void run() {
		int n = in.nextInt();
		int s = in.nextInt();
		int[] arr = new int[n];
		for (int i = 0; i < n; ++i) {
			arr[i] = in.nextInt();
		}
		Arrays.sort(arr);
		int sum = 0;
		for (int i = 0; i < n-1; ++i) {
			sum += arr[i];
		}
		if (sum > s) {
			out.println("NO");
		} else {
			out.println("YES");
		}
		out.flush();
	}
	
}

B.暴力枚舉b的行數，判斷是否能構成a。

import java.io.PrintWriter;
import java.util.Arrays;
import java.util.Scanner;

public class Codeforces {

	public static void main(String[] args) {
		new TaskB().run();
	}
	
}

class TaskB {
	
	Scanner in = new Scanner(System.in);
	PrintWriter out = new PrintWriter(System.out);
	int[][] a;
	int n,m;
	public void run() {
		n = in.nextInt();
		m = in.nextInt();
		a = new int[n][m];
		for (int i = 0; i < n; ++i) {
			for (int j = 0; j < m; ++j) {
				a[i][j] = in.nextInt();
			}
		}
		int ans = 1;
		while(ans < n && !judge(ans))++ans;
		out.println(ans);
		out.flush();
	}
	
	boolean judge(int k) {
		if (2*k > n) {
			return false;
		}
		for (int i = 0; i < k; ++i) {
			for (int j = 0; j < m; ++j) {
				if (a[i][j] != a[2*k-1-i][j]) {
					return false;
				}
			}
		}
		if (2*k == n)return true;
		return judge(k*2);
	}
	
}

C。暴力枚舉結果的起點和終點，將區間內的數於區間外的數交換，求最大值。

import java.io.PrintWriter;
import java.util.Arrays;
import java.util.Scanner;

public class Codeforces {

	public static void main(String[] args) {
		new TaskC().run();
	}
	
}

class TaskC {
	
	Scanner in = new Scanner(System.in);
	PrintWriter out = new PrintWriter(System.out);
	int[] a;
	int n,m;
	public void run() {
		n = in.nextInt();
		m = in.nextInt();
		a = new int[n];
		int ans = 0xafffffff;
		for (int i = 0; i < n; ++i) {
			a[i] = in.nextInt();
		}
		for (int i = 0; i < n; ++i) {
			for (int j = i; j < n; ++j) {
				ans = Math.max(ans,judge(i,j));
			}
		}
		out.println(ans);
		out.flush();
	}
	
	void asign(int begin, int l, int r, int[] arr) {
		for (int i = l; i <= r; ++i) {
			arr[begin] = a[i];
			begin++;
		}
	}
	
	int judge(int l, int r) {
		int[] cal = new int[r-l+1];
		asign(0, l, r, cal);
		if (cal.length < n) {
			int[] lef = new int[n-cal.length];
			asign(0, 0, l-1, lef);
			asign(l, r+1, n-1, lef);
		
			Arrays.sort(cal);
			Arrays.sort(lef);
			int j = lef.length-1;
			for (int i = 0; i < cal.length && j >= 0 && lef[j] >= cal[i] && lef.length-1-j < m; ++i) {
				cal[i] = lef[j];
				--j;
			}
		}
		int ret = 0;
		for (int i = 0; i < cal.length; ++i) {
			ret += cal[i];
		}
		return ret;
	}
}