Leetcode Exercises

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This is a leetcode algorithm list for me to track my thought and solutions.

1. Two-Sum

Problem Description: 1. Two-Sum

1.1. Golang

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func twoSum(nums []int, target int) []int {
    size := len(nums)
    for i := 0; i < size; i++ {
        for j := i + 1; j < size; j++ {
            if nums[i] + nums[j] == target {
                result := []int{i, j}
                sort.Slice(result, func(i, j int) bool {
                    return result[i] <= result[j]
                })
                return result
            }
        }
    }
    return []int{0, 0}
}

1.2. Java

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class Solution {
    public int[] twoSum(int[] numbers, int target) {
        int [] res = new int[2];
        if(numbers==null||numbers.length<2)
            return res;
        HashMap<Integer,Integer> map = new HashMap<Integer,Integer>();
        for(int i = 0; i < numbers.length; i++){
            if(!map.containsKey(target-numbers[i])){
                map.put(numbers[i],i);
            }else{
                res[0]= map.get(target-numbers[i]);
                res[1]= i;
                break;
            }
        }
        return res;
    }
}

2. Path Sum

Problem Description: 112. Path Sum

2.1. Java

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/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    /*
    Test if there is a path from current node to leaf node
    */
    public boolean hasPathSum(TreeNode root, int sum) {
        if(root == null) return false;
        if(root.left == null && root.right == null) {
            if (sum == root.val) return true;
            else return false;
        }
        sum = sum - root.val; // take value from current root node
        return hasPathSum(root.left, sum) || hasPathSum(root.right, sum);
    }
}

3. Reverse Words in a String

Problem Description: 151. Reverse Words in a String

3.1. Java

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public class Solution {
    
    public String reverseWords(String s) {
        s = s.trim();
        if(s.equals("")) return "";
        String[] str_arr = s.split("\\s+");
        StringBuilder sb = new StringBuilder("");
        for(int i = str_arr.length-1; i>0; i--) {
            sb.append(str_arr[i] + " ");
        }
        sb.append(str_arr[0]);
        return sb.toString();
    }
}

4. Combine Two Tables

Problem Description: 175. Combine Two Tables

4.1. MySQL

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# Write your MySQL query statement below
select p.FirstName, p.LastName, a.City, a.State from Person as p 
  left join Address as a 
  on 
  p.PersonId = a.PersonId;

5. Fizz Buzz

Problem Description: 412. Fizz Buzz

5.1. Java

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public class Solution {
    private boolean multiple(int i, int modValue){
        return i%modValue==0;
    }
    public List<String> fizzBuzz(int n) {
        List<String> list = new ArrayList();
        for(int i = 1;i <= n;i++) {
            String str = String.valueOf(i);
            if(multiple(i,3) && multiple(i,5)) {
                list.add("FizzBuzz");
            }
            else if(multiple(i,3) && !multiple(i,5)) {
                list.add("Fizz");
            }
            else if(!multiple(i,3) && multiple(i,5)) {
                list.add("Buzz");
            }
            else {
                list.add(str);
            }
        }
        return list;
        
    }
}
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