1.苹果分堆 

计算累加小组成员数，结合二分查找，复杂度O( min(n, mlogn) )

package wangyi123;import java.util.Scanner;public class groupNum {public static void main(String[] args) {Scanner sc = new Scanner(System.in);while (sc.hasNext()) {int n = sc.nextInt();int[] arr = new int[n];arr[0] = sc.nextInt();for (int i = 1; i < n; i++) {arr[i] = arr[i - 1] + sc.nextInt();}int m = sc.nextInt();int query = 0;int index = 0;for (int i = 0; i < m; i++) {query = sc.nextInt();index = search(arr, query);System.out.print(index + " ");}}sc.close();}public static int search(int a[], int target) {int left = 0;int right = a.length - 1;int mid = 0;while (left < right) {mid = left + (right - left) / 2;if (target >= a[mid]) {left = ++mid;} else {right = mid;}}return left + 1;}
}

2.字符串理论 

. 

package wangyi123;import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;public class straz {public static void main(String[] args) {Scanner sc = new Scanner(System.in);int n = sc.nextInt();int m = sc.nextInt();int k = sc.nextInt();List<String> result = new ArrayList<>();dfs(n, m, k, "", result);System.out.println(result);}static boolean flag = false;public static void dfs(int n, int m, int k, String s, List<String> result) {if (n == 0 && m == 0) {result.add(s);if (result.size() == k) {flag = true;}return;}if (flag) {return;}if (n > 0) {dfs(n - 1, m, k, s + 'a', result);}if (m > 0) {dfs(n, m - 1, k, s + 'z', result);}}
}

3.上课瞌睡

package wangyi123;import java.util.Scanner;public class sleep {public static void main(String[] args) {Scanner sc = new Scanner(System.in);int n = sc.nextInt();int k = sc.nextInt();int[] a = new int[n];int[] t = new int[n];for (int i = 0; i < n; i++)a[i] = sc.nextInt();int now = 0;for (int i = 0; i < n; i++) {t[i] = sc.nextInt();now += t[i] * a[i];}int res = now;for (int i = 0; i < n; i++) {if (t[i] == 0) {now += a[i];}if (i + 1 >= k) {res = Math.max(res, now);if (t[i + 1 - k] == 0) {now -= a[i + 1 - k];}}}System.out.println(res);}}