LeetCode01:Two Sum Java实现

原题目：

Given an array of integers, return indices of the two numbers such that they add up to a specific target.

You may assume that each input would have exactly one solution

Example:

Given nums = [2, 7, 11, 15], target = 9,

Because nums[0] + nums[1] = 2 + 7 = 9,

return [0, 1].

 对于一个给定的整数数组和一个目标值，求出数组中两个数之和等于目标值，输出数组中这两个数的下标

算法分析：

        算法1.时间复杂度为O（n^2）.

        采用两个指针i和j,i和j分别指向数组中前两个值，判断i和j所指值之和是否等于目标函数，若不等于，则向后移动i和j，直到找到两个数之和等于目标函数为止。输出i和j即可

遇到问题及解决方案：

1.没有考虑目标值是0的情况

        如果直接判断两个数相加的值是否等于目标值，则会忽略目标值为0，数组中也同样包含0的情况，所有需要先判断目标值是否为0。如果目标值为0，则直接找出两个0并输出即可。

if(target == 0 && nums[i] == 0&&nums[j] == 0){        

                    tmp[0] = i;

                    tmp[1] = j;

                    return tmp;

                }  

LeetCode提交源码：

public class Solution {
    public int[] twoSum(int[] nums, int target) {
       if(nums == null )
			return null;
		int[] tmp = new int[2];
//		int i = 0;
//		int j = 0;
		for(int i = 0; i < nums.length; i++){ 
			for(int j = i+1; j < nums.length; j++){
			    
			    if(target == 0 && nums[i] == 0&&nums[j] == 0){
					tmp[0] = i;
					tmp[1] = j;
					return tmp;
				}
				if(nums[i] + nums[j] == target){
					tmp[0] = j;
					tmp[1] = i;
					
				}
			}
		}
		System.out.println(tmp[0] + " " + tmp[1]);
		return tmp;
    }
}

Submission Details：

 

完整运行程序：

package org.GuoGuoFighting.LeetCode1;
import java.util.Scanner;
class Solution1{
	public int[] twoSum(int[] nums,int target){
		if(nums == null )
			return null;
		int[] tmp = new int[2];
//		int i = 0;
//		int j = 0;
		for(int i = 0; i < nums.length; i++){ 
			for(int j = i+1; j < nums.length; j++){
//				if(nums[j] == target && nums[i] == target && i != j){		//如果输入的target包含在数组中，则返回这两个值
				if(target == 0 && nums[i] == 0&&nums[j] == 0){		//如果输入的target包含在数组中，则返回这两个值
					tmp[0] = i;
					tmp[1] = j;
					return tmp;
				}
					
				if(nums[i] + nums[j] == target){
					tmp[0] = i;
					tmp[1] = j;
					
				}
			}
			
		}
		System.out.println(tmp[0] + " " + tmp[1]);
		return tmp;
	}
}
public class TwoSum {
	public static void main(String[] args){
		Scanner scanner = new Scanner(System.in);
		System.out.println("请输入一个整形数组，用空格隔开：");
		String str =  scanner.nextLine();
		System.out.println("请输入要找的目标k:");
		int k = scanner.nextInt();
		
		String[] tmp = str.split(" ");
		int[] arrays = new int[tmp.length];
		for(int i = 0; i < arrays.length;i++){
			arrays[i] = Integer.parseInt(tmp[i]);
		}
		
		scanner.close();
		Solution1 solution1 = new Solution1();
		int[] ansarray = solution1.twoSum(arrays, k);			//将输出的数组打印
		System.out.println("这两个数是：" + ansarray[0] + "," + ansarray[1]);
	}
}

程序运行结果：