拼多多-2019秋招笔试【第一批】

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************************************【第一题：数组中的最长山谷】***************************************

方法一：堆栈 

package pinduoduo;
import java.util.Scanner;
import java.util.Stack;

public class MountainValley {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        Stack s1 = new Stack<>();//左坡
        Stack s2 = new Stack<>();//右坡
        int max = Integer.MIN_VALUE;
        while (sc.hasNext()) {
            while (sc.hasNext()) {
                int a = sc.nextInt();
                if (s1.isEmpty()) {
                    s1.push(a);
                } else {
                    if (a < s1.peek()) {
                        s1.push(a);
                    } else {
                        s2.push(a);
                        break;
                    }
                }

            }
            int b = Integer.MAX_VALUE;    //存储山谷后的一个值
            while (sc.hasNext()) {
                int a = sc.nextInt();
                if (s2.isEmpty()) {
                    s2.push(a);
                } else {
                    if (a > s2.peek()) {
                        s2.push(a);
                    } else {
                        b = a;
                        break;
                    }
                }

            }
            if (s1.size() > 1 && s2.size() > 0) {
                if (max < s1.size() + s2.size()) {
                    max = s1.size() + s2.size();
                }
                s1.clear();
                s1.push(s2.peek());
                if (b != Integer.MAX_VALUE) {
                    s1.push(b);
                }
                s2.clear();
            } else {
                s1.clear();
                if (!s2.isEmpty()) {
                    s1.push(s2.peek());
                    if (b != Integer.MAX_VALUE) {
                        s1.push(b);
                    }
                    s2.clear();
                }
            }
        }
        System.out.println(max);
    }

}

方法二：直接法

public static int longestMountain(int[] A) {
        int res = 0, up = 0, down = 0;
        for (int i = 1; i < A.length; ++i) {
            if (up > 0 && A[i - 1] > A[i] || A[i - 1] == A[i])
                up = down = 0;
            if (A[i - 1] < A[i])
                up++;
            if (A[i - 1] > A[i])
                down++;
            if (up > 0 && down > 0 && up + down + 1 > res)
                res = up + down + 1;
        }
        return res;
    }

 

*************************************【第二题：二维生物】************************************************

 

package pinduoduo;
import java.util.Scanner;
//二维生物
public class TwoDimenBiology {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        long target = Math.abs(sc.nextLong());
        long sum = 0;
        long step = 1;// 步长
        while (sum < target) {// 查找超过去的sum
            sum += step;
            step++;
        }
        step--;
        if (sum == target) {
            System.out.println(step);
        } else {
            step += (sum - target) * 2;// 向前+向后=sum-1,一共(sum-target）*2次
            System.out.println(step);
        }
    }

}

*************************************【第三题：字符串构造】************************************************ 

package pinduoduo;
import java.util.Scanner;
//字符串构造
public class StrMake {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String s = sc.nextLine();
		System.out.println(make(s));
	}

	public static String make(String s) {
		for (int i = 1; i < s.length(); i++) {
			String str = s.substring(0, i);
			StringBuffer sb = new StringBuffer();
			for (int j = 0; j < s.length() / i; j++) {
				sb.append(str);
			}
			if (sb.toString().equals(s)) {
				return str;
			}
		}
		return s;
	}

}