题目内容
There is an array A consisting of N integers. What is the maximum sum of two integers from A that share their first and last digits? For example, 1007 and 167 share their first (1) and last (7) digits, whereas 2002 and 55 do not.Write a function:class Solution { public int solution(int[] A); }that, given an array A consisting of N integers, returns the maximum sum of two integers that share their first and last digits. If there are no two integers that share their first and last digits, the function should return -1.Examples:1. Given A = [130, 191, 200, 10], the function should return 140. The only integers in A that share first and last digits are 130 and 10.2. Given A = [405, 45, 300, 300], the function should return 600. There are two pairs of integers that share first and last digits: (405, 45) and (300, 300). The sum of the two 300s is bigger than the sum of 405 and 45.3. Given A = [50, 222, 49, 52, 25], the function should return -1. There are no two integers that share their first and last digits.4. Given A = [30, 909, 3190, 99, 3990, 9009], the function should return 9918. Write an efficient algorithm for the following assumptions:* N is an integer within the range [1 .. 100,000);* each element of array A is an integer within the range [10..1,000,000,000).
解法一
思路
创建IntegerPair类存放第一个数字和最后一个数字相同的整型数字对。然后遍历数组A。借助Map来构造所有的IntegerPair. 最后求出最大的IntegerPair.
java 代码实现
public class Task2 {private class IntegerPair{int firstNumber;int secondNumber;public IntegerPair(int firstNumber){this.firstNumber = firstNumber;}void replaceMinimumNumber(int number){int minimum = firstNumber>secondNumber? secondNumber: firstNumber;if (minimum < number){if (firstNumber>secondNumber){this.secondNumber = number;}else{this.firstNumber = number;}}}int getSum(){if (secondNumber!=0){return firstNumber + secondNumber;}else{return -1;}}}private String getKey(int number){char[] chars = String.valueOf(number).toCharArray();return Character.valueOf(chars[0]).toString()+Character.valueOf(chars[chars.length-1]).toString();}public int solution(int[] A){Map<String, IntegerPair> maps = new HashMap<>();for (int i=0; i< A.length ; i++){String key = getKey(A[i]);IntegerPair integerPair = maps.get(key);if(integerPair==null){maps.put(key, new IntegerPair(A[i]));}else{if(integerPair.secondNumber==0){integerPair.secondNumber = A[i];}else{integerPair.replaceMinimumNumber(A[i]);}}}int maxSum = -1;for(String key: maps.keySet()){IntegerPair twoIntegerMap = maps.get(key);if (twoIntegerMap.getSum() >maxSum){maxSum = twoIntegerMap.getSum();}}return maxSum;}public static void main(String[] args) {Task2 task = new Task2();int[] test = new int[]{130, 191, 200, 10};System.out.println(task.solution(test)); // Output: 140test = new int[]{405, 45, 300, 300};System.out.println(task.solution(test)); // Output: 600test = new int[]{50, 222, 49, 52, 25};System.out.println(task.solution(test)); // Output: -1test = new int[]{30, 909, 3190, 99, 3990, 9009};System.out.println(task.solution(test)); // Output: 9918}
}
)
