算法经典问题————两数之和

import java.util.HashMap;

public class DoubleSum {
    public static void main(String[] args) {
    int[] test = {6,7,5,4,9,8};
    int goals = 13;
    doubleSum(test,goals);
    separate();
    doubleSum2(test,goals);
    }

    //算法一：暴力算法
    public static void doubleSum(int[] array,int goal){
        for (int i = 0; i < array.length; i++) {
            int temp = goal - array[i];
            for (int j = i+1; j < array.length; j++) {
                if(array[j]==temp)
                {
                    System.out.println("["+i+","+j+"]");
                }
            }
        }
    }

    //散列算法
    public static void doubleSum2(int[] array,int goal){
        HashMap map = new HashMap();
        for (int i = 1; i < array.length ; i++) {
            map.put(array[i],i);
        }
        for (int i = 0; i < array.length-1; i++) {
            int temp = goal - array[i];
            if(map.get(temp)!=null && map.get(temp)>i){
                System.out.println("["+i+","+map.get(temp)+"]");
            }
        }
    }

    public static void separate(){
        System.out.println();
        System.out.println("--------------------------");
    }
}

这一串代码暂时没考虑重复问题

结果：

上面是测试用

下面是Leetcode通过测试代码段源代码：

//Leetcode 通过样式
class Solution {
    public int[] twoSum(int[] nums, int target) {
        HashMap map = new HashMap();
        for (int i = 1; i < nums.length ; i++) {
            map.put(nums[i],i);
        }
        for (int i = 0; i < nums.length-1; i++) {
            int temp = target - nums[i];
            if(map.get(temp)!=null && map.get(temp)>i){
                return new int[]{i,map.get(temp)};
            }
        }
        return new int[]{};
    }