[Boj]3273번 : 두 수의 합

1. problem :

https://www.acmicpc.net/problem/3273

 

 

2. solution 1 :

def count_pairs_with_sum(arr, x):
    arr.sort()
    left = 0
    right = len(arr) - 1
    count = 0
    
    while left < right:
        current_sum = arr[left] + arr[right]
        if current_sum == x:
            count += 1
            left += 1
            right -= 1
        elif current_sum < x:
            left += 1
        else:
            right -= 1
            
    return count

# 입력 받기
n = int(input())
arr = list(map(int, input().split()))
x = int(input())

# 쌍의 개수 출력
print(count_pairs_with_sum(arr, x))

two-pointer를 이용한 방법. 

 

3. solution 2 :

n = int(input())
nums = list(map(int,input().split()))
x = int(input())
count = 0 
hashMap = {}
for i in range(n):
    target = x - nums[i]
    if target in hashMap:
        if hashMap[target] == 1 :
            del hashMap[target]
        else:
            hashMap[target] -= 1 
        count += 1 
    else:
        hashMap[nums[i]] = 1

hashMap을 이용한 방법