_170_TwoSumIII_Datastructuredesign.java

package leetcode_1To300;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

/**
 * 本代码来自 Cspiration，由 @Cspiration 提供
 * 题目来源：http://leetcode.com
 * - Cspiration 致力于在 CS 领域内帮助中国人找到工作，让更多海外国人受益
 * - 现有课程：Leetcode Java 版本视频讲解（1-900题）（上）（中）（下）三部
 * - 算法基础知识（上）（下）两部；题型技巧讲解（上）（下）两部
 * - 节省刷题时间，效率提高2-3倍，初学者轻松一天10题，入门者轻松一天20题
 * - 讲师：Edward Shi
 * - 官方网站：https://cspiration.com
 * - 版权所有，转发请注明出处
 */
public class _170_TwoSumIII_Datastructuredesign {

    /**
     * 170. Two Sum III - Data structure design
     * Design and implement a _1_TwoSum class. It should support the following operations: add and find.

     add - Add the number to an internal data structure.
     find - Find if there exists any pair of numbers which sum is equal to the value.

     For example,
     add(1); add(3); add(5);
     find(4) -> true
     find(7) -> false

     */

    /** Initialize your data structure here. */

    private HashMap<Integer, Integer> map;

    // 构造函数，leetcode中是TwoSum
    public _170_TwoSumIII_Datastructuredesign() {
        map = new HashMap<>();
    }

    /** Add the number to an internal data structure.. */
    public void add(int number) {
        if (!map.containsKey(number)) {
            map.put(number, 1);
        } else {
            map.put(number, map.get(number) + 1);
        }
    }

    // time : O(n)
    /** Find if there exists any pair of numbers which sum is equal to the value. */
    public boolean find(int value) {
        for (Map.Entry<Integer, Integer> entry : map.entrySet()) {
            int i = entry.getKey();
            int j = value - i;
            if ((i == j && entry.getValue() > 1) || (i != j && map.containsKey(j))) {
                return true;
            }
        }
        return false;
    }

    /**------------------------------------------分割线--------------------------------------------------**/

    //构造函数，leetcode中是TwoSum, map 在上一个解法中有

    private List<Integer> list;

    public void TwoSum() {
        map = new HashMap<>();
        list = new ArrayList<>();
    }

    public void add2(int number) {
        if (!map.containsKey(number)) {
            map.put(number, 1);
            list.add(number);
        } else {
            map.put(number, map.get(number) + 1);
        }
    }

    // time : O(n)
    public boolean find2(int value) {
        for (Integer num1 : list) {
            int num2 = value - num1;
            if ((num1 == num2 && map.get(num1) > 1) || (num1 != num2 && map.containsKey(num2))) {
                return true;
            }
        }
        return false;
    }
}