△9023▲

-- 1.Introduction
SELECT name, continent, population FROM world

-- 2.Large Countries
SELECT name FROM world
WHERE population >= 200000000

-- 3.Per capita GDP (1인당 국내 총생산)
SELECT name, GDP/population
FROM world
WHERE population >= 200000000

-- 4.South America In millions
SELECT name, population/1000000
FROM world
WHERE continent='South America'

-- 5.France, Germany, Italy
SELECT name, population
FROM world
WHERE name IN ('France', 'Germany', 'Italy')

-- 6.United
SELECT name
FROM world
WHERE name LIKE '%United%'

-- 7.Two ways to be big
SELECT name, population, area
FROM world
WHERE area >= 3000000 OR population >=250000000

-- 8.One or the other (but not both)
SELECT name, population, area
FROM world
WHERE (area > 3000000 AND population<250000000) OR (area < 3000000 AND population>250000000) 

-- 9.Rounding
SELECT name, ROUND(population/1000000,2), ROUND(gdp/1000000000,2)
FROM world
WHERE continent='South America'

-- 10.Trillion dollar economies
SELECT name, ROUND(gdp/population, -3)
FROM world
WHERE gdp>1000000000000

-- 11.Name and capital have the same length
-- Correct 확인 안됨..
SELECT name, capital 
FROM world 
WHERE LEN(name) = LEN(capital);

-- 12.Matching name and capital
-- <> as the NOT EQUALS
SELECT name, capital
FROM world
WHERE LEFT(name,1)= LEFT(capital,1)
	AND name<>capital

-- 13.All the vowels
SELECT name
  FROM world
WHERE name LIKE '%a%'
  AND name LIKE '%e%'
  AND name LIKE '%i%'
  AND name LIKE '%o%'
  AND name LIKE '%u%'
  AND name NOT LIKE '% %'

1. Select the code which produces this table

SELECT name, population
  FROM world
 WHERE population BETWEEN 1000000 AND 1250000

2. Pick the result you would obtain from this code:

3. Select the code which shows the countries that end in A or L

SELECT name FROM world
 WHERE name LIKE '%a' OR name LIKE '%l'

4. Pick the result from the query

5. Here are the first few rows of the world table:

Pick the result you would obtain from this code:

6. Select the code that would show the countries with an area larger than 50000 and a population smaller than 10000000

SELECT name, area, population
  FROM world
 WHERE area > 50000 AND population < 10000000

7. Select the code that shows the population density(인구밀도) of China, Australia, Nigeria and France

SELECT name, population/area
  FROM world
 WHERE name IN ('China', 'Nigeria', 'France', 'Australia')

-- 1. Introducing the world table of countries

SELECT population FROM world
  WHERE name = 'Germany'
  
-- 2. Scandinavia
  
SELECT name, population FROM world
  WHERE name IN ('Sweden', 'Norway', 'Denmark');
  
-- 3. Just the right size
  
SELECT name, area FROM world
  WHERE area BETWEEN 200000 AND 250000

https://www.acmicpc.net/problem/2252

- PASS

#include <string>
#include <vector>
#include <iostream>
#include <algorithm>

using namespace std;

vector<vector<int>> vec;
vector<int> result;
int N, M;
int visit[32001];

void dfs(int num) {
	visit[num] = 1;

    for (auto i : vec[num]) {
        if (visit[i])
            continue;
        dfs(i);
    }

    result.push_back(num);
}

int main() {

    cin >> N >> M;

	vec.resize(N + 1);

    for (int i = 0; i < M; i++) {
        int A, B;
        cin >> A >> B;
		vec[A].push_back(B);
    }

    for (int i = 1; i <= N; i++) {
        if (visit[i]==0)
            dfs(i);
    }

	for (int i = N - 1; i >= 0; i--)
		cout << result[i] << " ";

    return 0;
}

- FAIL

#include <string>
#include <vector>
#include <iostream>
#include <algorithm>

using namespace std;

int main() {

	vector<int> row;

	int N, M;

	cin >> N >> M;

	for (int i = 0; i < M; i++) {
		int A, B;
		cin >> A >> B;
		int flag = 0;
		for (int j = 0; j < row.size(); j++) {
			if (row[j] == B) {
				row.insert(row.begin() + j, A);
				flag = 1;
				break;
			}
		}

		if (flag == 0) {
			row.push_back(A);
			row.push_back(B);
		}
	}

	for (int i = 0; i < N; i++)
		cout << row[i] << " ";
        
    return 0;
}

https://www.acmicpc.net/problem/1197

#include <iostream>
#include <vector>
#include <algorithm>
#include <queue>

using namespace std;

vector<pair<int, pair<int, int>>> vec;
int boss[10001];

int findBoss(int a) {
	if (boss[a] == a)
		return a;
	else
		return boss[a] = findBoss(boss[a]);
}

void setUnion(int a, int b) {
	a = findBoss(a);
	b = findBoss(b);

	if (a != b)
		boss[b] = a;
}


int main() {

	ios::sync_with_stdio(false);
	cin.tie(NULL);
	cout.tie(NULL);

	int V, E;
	cin >> V >> E;

	for (int i = 0; i < E; i++) {
		int a, b, c;
		cin >> a >> b >> c;

		vec.push_back(make_pair(c, make_pair(a, b)));
	}

	sort(vec.begin(), vec.end());

	for (int i = 1; i <= V; i++) {
		boss[i] = i;
	}

	int result = 0;
	for (int i = 0; i < E; i++) {
		int a = vec[i].second.first;
		int b = vec[i].second.second;
		if (findBoss(a) != findBoss(b)) {
			setUnion(a, b);
			result += vec[i].first;
		}
	}

	cout << result;

	return 0;
}

https://www.acmicpc.net/problem/5052

// https://www.acmicpc.net/problem/5052

#include <iostream>
#include <algorithm>
#include <string>

using namespace std;

int main() {
	int t, n;
	cin >> t;
	for (int i = 0; i < t; i++) {
		cin >> n;
		string input[10000];
		for (int j = 0; j < n; j++) {
			cin >> input[j];
		}
		
		sort(input, input + n);

		int flag = 0;
		for (int i = 0; i < n-1; i++) {
			string tmp1 = input[i];
			string tmp2 = input[i + 1];

			if (tmp1.size() > tmp2.size())
				continue;

			else if(tmp1 == tmp2.substr(0,tmp1.size())) {
				cout << "NO" << "\n";
				flag = 1;
				break;
			}
		}

		if(flag==0)
			cout << "YES" << "\n";
	}

	return 0;
}

https://www.acmicpc.net/problem/21924

#include <iostream>
#include <vector>
#include <algorithm>
#include <queue>

using namespace std;

vector<pair<int, pair<int, int>>> vec;
int boss[100001];
int visit[100001] = { 0 };

int findBoss(int a) {
	if (boss[a] == a)
		return a;
	else
		return boss[a] = findBoss(boss[a]);
}

void setUnion(int a, int b) {
	a = findBoss(a);
	b = findBoss(b);

	if (a != b)
		boss[b] = a;
}

int main() {

	ios::sync_with_stdio(false);
	cin.tie(NULL);
	cout.tie(NULL);

	int N, M;
	cin >> N >> M;

	long long sum = 0;
	for (int i = 0; i < M; i++) {
		int a, b, c;
		cin >> a >> b >> c;
		sum += c;

		vec.push_back(make_pair(c, make_pair(a, b)));
	}

	sort(vec.begin(), vec.end());

	for (int i = 1; i <= N; i++) {
		boss[i] = i;
	}

	long long result = 0;
	for (int i = 0; i < M; i++) {
		int a = vec[i].second.first;
		int b = vec[i].second.second;
		if (findBoss(a) != findBoss(b)) {
			setUnion(a, b);
			visit[a] = 1;
			visit[b] = 1;
			result += vec[i].first;
		}
	}

	for (int i = 1; i < N; i++) {
		if (findBoss(i) != findBoss(i+1)) {
			cout << -1;
			return 0;
		}
	}

	cout << sum - result;

	return 0;
}

https://www.acmicpc.net/problem/14716

#include <iostream>
#include <vector>
#include <algorithm>
#include <queue>

using namespace std;

int M, N;
int cnt = 0;
int map[251][251] = { 0 };
int visit[251][251] = { 0 };

void dfs(int y, int x) {
	int direct[8][2] = {
		-1,-1,
		-1,0,
		-1,1,
		0,-1,
		0,1,
		1,-1,
		1,0,
		1,1
	};

	for (int i = 0; i < 8; i++) {
		int dy = y + direct[i][0];
		int dx = x + direct[i][1];

		if (dy < 0 || dx < 0 || dy >= M || dx >= N)
			continue;

		if (visit[dy][dx] == 1)
			continue;

		if (map[dy][dx] == 1) {
			visit[dy][dx] = 1;
			dfs(dy, dx);
		}
	}
}

int main() {

	ios_base::sync_with_stdio(false); cout.tie(NULL); cin.tie(NULL);

	cin >> M >> N;

	for (int i = 0; i < M; i++) {
		for (int j = 0; j < N; j++) {
			cin >> map[i][j];
		}
	}

	for (int i = 0; i < M; i++) {
		for (int j = 0; j < N; j++) {
			if (map[i][j] == 1 && visit[i][j] != 1) {
				dfs(i, j);
				visit[i][j] = 1;
				cnt++;
			}
		}
	}

	cout << cnt;

	return 0;
}