github demo : https://github.com/happyjiatai/LeetCodeTest/tree/master/1_two_sum

1. search

Use Baidu Search

The first link is leetCode international? The second is the Chinese version. I have entered the Chinese version.

 

2. interface

 

3. topic

Just click the sum of the first two numbers

3.1 coding

class Solution {
    public int[] twoSum(int[] nums, int target) {
        for(int i = 0; i < nums.length - 1; i++){
            for(int j = i + 1; j < nums.length; j++){
                if(target == nums[i] + nums[j]){
                    return new int[]{i, j};
                }
            }
        }
        return null;
    }
}

3.2 write test cases

Check the custom test case and write your own input

 

3.3 execution code

 

3.4 Android studio test

package com.example.a1_two_sum;


public class MyClass {
    public static void main(String args[]){
        Solution solution = new Solution();
        int[] result = solution.twoSum(new int[]{12,32,54,1}, 55);
        if (null == result){
            System.out.println("null");
        }else{
            StringBuilder stringBuilder = new StringBuilder();
            stringBuilder.append("[");
            for(int i : result){
                stringBuilder.append(i);
                stringBuilder.append(",");
            }
            stringBuilder.deleteCharAt(4);
            stringBuilder.append("]");
            System.out.println(stringBuilder);
        }
    }
}

class Solution{
    public int[] twoSum(int[] nums, int target) {
        for(int i = 0; i < nums.length - 1; i++){
            for(int j = i + 1; j < nums.length; j++){
                if(target == nums[i] + nums[j]){
                    return new int[]{i, j};
                }
            }
        }
        return null;
    }
}

 

3.5 submission

 

3.5.1 official use cases

 

3.5.2 official answer

In method 2, hashmap is used to eliminate the second level traversal of violent traversal, because the location of hashmap is determined by the hash value, so it is not necessary to traverse in turn. Method 3 is the optimization based on method 2.

 

4. summary

emmm, one week question?