[Silver V] Title: 포린드롬, Time: 104 ms, Memory: 37384 KB -BaekjoonHub

Author: Ja2Hw

백준/Silver/33690. 포린드롬/README.md

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+# [Silver V] 포린드롬 - 33690 
+
+[문제 링크](https://www.acmicpc.net/problem/33690) 
+
+### 성능 요약
+
+메모리: 37384 KB, 시간: 104 ms
+
+### 분류
+
+애드 혹, 브루트포스 알고리즘, 수학
+
+### 제출 일자
+
+2025년 5월 2일 18:55:57
+
+### 문제 설명
+
+<p>싱글벙글 즐거운 UDPC 수학 수업 시간. 포닉스는 아래와 같은 내용을 배웠다.</p>
+
+<ul>
+	<li>음이 아닌 정수 <mjx-container class="MathJax" jax="CHTML" style="font-size: 104.6%; position: relative;"><mjx-math class="MJX-TEX" aria-hidden="true"><mjx-mi class="mjx-i"><mjx-c class="mjx-c1D443 TEX-I"></mjx-c></mjx-mi></mjx-math><mjx-assistive-mml unselectable="on" display="inline"><math xmlns="http://www.w3.org/1998/Math/MathML"><mi>P</mi></math></mjx-assistive-mml><span aria-hidden="true" class="no-mathjax mjx-copytext">$P$</span></mjx-container>에 대해, <mjx-container class="MathJax" jax="CHTML" style="font-size: 104.6%; position: relative;"><mjx-math class="MJX-TEX" aria-hidden="true"><mjx-mi class="mjx-i"><mjx-c class="mjx-c1D443 TEX-I"></mjx-c></mjx-mi></mjx-math><mjx-assistive-mml unselectable="on" display="inline"><math xmlns="http://www.w3.org/1998/Math/MathML"><mi>P</mi></math></mjx-assistive-mml><span aria-hidden="true" class="no-mathjax mjx-copytext">$P$</span></mjx-container>의 숫자들을 거꾸로 읽어도 원래의 <mjx-container class="MathJax" jax="CHTML" style="font-size: 104.6%; position: relative;"><mjx-math class="MJX-TEX" aria-hidden="true"><mjx-mi class="mjx-i"><mjx-c class="mjx-c1D443 TEX-I"></mjx-c></mjx-mi></mjx-math><mjx-assistive-mml unselectable="on" display="inline"><math xmlns="http://www.w3.org/1998/Math/MathML"><mi>P</mi></math></mjx-assistive-mml><span aria-hidden="true" class="no-mathjax mjx-copytext">$P$</span></mjx-container>와 같다면 <mjx-container class="MathJax" jax="CHTML" style="font-size: 104.6%; position: relative;"><mjx-math class="MJX-TEX" aria-hidden="true"><mjx-mi class="mjx-i"><mjx-c class="mjx-c1D443 TEX-I"></mjx-c></mjx-mi></mjx-math><mjx-assistive-mml unselectable="on" display="inline"><math xmlns="http://www.w3.org/1998/Math/MathML"><mi>P</mi></math></mjx-assistive-mml><span aria-hidden="true" class="no-mathjax mjx-copytext">$P$</span></mjx-container>을 <strong>팰린드롬 수</strong>라고 한다. (단, 여러 자릿수로 구성된 수는 <mjx-container class="MathJax" jax="CHTML" style="font-size: 104.6%; position: relative;"><mjx-math class="MJX-TEX" aria-hidden="true"><mjx-mn class="mjx-n"><mjx-c class="mjx-c30"></mjx-c></mjx-mn></mjx-math><mjx-assistive-mml unselectable="on" display="inline"><math xmlns="http://www.w3.org/1998/Math/MathML"><mn>0</mn></math></mjx-assistive-mml><span aria-hidden="true" class="no-mathjax mjx-copytext">$0$</span></mjx-container>으로 시작할 수 없다.)</li>
+</ul>
+
+<p>예를 들어 <mjx-container class="MathJax" jax="CHTML" style="font-size: 104.6%; position: relative;"><mjx-math class="MJX-TEX" aria-hidden="true"><mjx-mn class="mjx-n"><mjx-c class="mjx-c31"></mjx-c><mjx-c class="mjx-c31"></mjx-c><mjx-c class="mjx-c31"></mjx-c></mjx-mn></mjx-math><mjx-assistive-mml unselectable="on" display="inline"><math xmlns="http://www.w3.org/1998/Math/MathML"><mn>111</mn></math></mjx-assistive-mml><span aria-hidden="true" class="no-mathjax mjx-copytext">$111$</span></mjx-container>, <mjx-container class="MathJax" jax="CHTML" style="font-size: 104.6%; position: relative;"><mjx-math class="MJX-TEX" aria-hidden="true"><mjx-mn class="mjx-n"><mjx-c class="mjx-c31"></mjx-c><mjx-c class="mjx-c37"></mjx-c><mjx-c class="mjx-c37"></mjx-c><mjx-c class="mjx-c31"></mjx-c></mjx-mn></mjx-math><mjx-assistive-mml unselectable="on" display="inline"><math xmlns="http://www.w3.org/1998/Math/MathML"><mn>1771</mn></math></mjx-assistive-mml><span aria-hidden="true" class="no-mathjax mjx-copytext">$1771$</span></mjx-container>은 팰린드롬 수이지만, <mjx-container class="MathJax" jax="CHTML" style="font-size: 104.6%; position: relative;"><mjx-math class="MJX-TEX" aria-hidden="true"><mjx-mn class="mjx-n"><mjx-c class="mjx-c31"></mjx-c><mjx-c class="mjx-c30"></mjx-c><mjx-c class="mjx-c30"></mjx-c></mjx-mn></mjx-math><mjx-assistive-mml unselectable="on" display="inline"><math xmlns="http://www.w3.org/1998/Math/MathML"><mn>100</mn></math></mjx-assistive-mml><span aria-hidden="true" class="no-mathjax mjx-copytext">$100$</span></mjx-container>은 팰린드롬 수가 아니다.</p>
+
+<p>수업이 끝난 후, 포닉스는 팰린드롬 수라는 개념이 너무 재미없다고 생각했고, 집에서 <strong>포린드롬 수</strong>라는 새로운 수를 만들었다. 포닉스의 포린드롬 수는 아래와 같이 정의된다.</p>
+
+<ul>
+	<li>음이 아닌 정수 <mjx-container class="MathJax" jax="CHTML" style="font-size: 104.6%; position: relative;"><mjx-math class="MJX-TEX" aria-hidden="true"><mjx-mi class="mjx-i"><mjx-c class="mjx-c1D443 TEX-I"></mjx-c></mjx-mi></mjx-math><mjx-assistive-mml unselectable="on" display="inline"><math xmlns="http://www.w3.org/1998/Math/MathML"><mi>P</mi></math></mjx-assistive-mml><span aria-hidden="true" class="no-mathjax mjx-copytext">$P$</span></mjx-container>에 대해, <mjx-container class="MathJax" jax="CHTML" style="font-size: 104.6%; position: relative;"><mjx-math class="MJX-TEX" aria-hidden="true"><mjx-mi class="mjx-i"><mjx-c class="mjx-c1D443 TEX-I"></mjx-c></mjx-mi></mjx-math><mjx-assistive-mml unselectable="on" display="inline"><math xmlns="http://www.w3.org/1998/Math/MathML"><mi>P</mi></math></mjx-assistive-mml><span aria-hidden="true" class="no-mathjax mjx-copytext">$P$</span></mjx-container>와 <mjx-container class="MathJax" jax="CHTML" style="font-size: 104.6%; position: relative;"><mjx-math class="MJX-TEX" aria-hidden="true"><mjx-mo class="mjx-n"><mjx-c class="mjx-c230A"></mjx-c></mjx-mo><mjx-texatom texclass="ORD"><mjx-mfrac><mjx-frac><mjx-num><mjx-nstrut></mjx-nstrut><mjx-mi class="mjx-i" size="s"><mjx-c class="mjx-c1D443 TEX-I"></mjx-c></mjx-mi></mjx-num><mjx-dbox><mjx-dtable><mjx-line></mjx-line><mjx-row><mjx-den><mjx-dstrut></mjx-dstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c31"></mjx-c><mjx-c class="mjx-c30"></mjx-c></mjx-mn></mjx-den></mjx-row></mjx-dtable></mjx-dbox></mjx-frac></mjx-mfrac></mjx-texatom><mjx-mo class="mjx-n"><mjx-c class="mjx-c230B"></mjx-c></mjx-mo></mjx-math><mjx-assistive-mml unselectable="on" display="inline"><math xmlns="http://www.w3.org/1998/Math/MathML"><mo fence="false" stretchy="false">⌊</mo><mrow data-mjx-texclass="ORD"><mfrac><mi>P</mi><mn>10</mn></mfrac></mrow><mo fence="false" stretchy="false">⌋</mo></math></mjx-assistive-mml><span aria-hidden="true" class="no-mathjax mjx-copytext">$\lfloor {P \over 10} \rfloor$</span></mjx-container>이 모두 팰린드롬 수일 때, <mjx-container class="MathJax" jax="CHTML" style="font-size: 104.6%; position: relative;"><mjx-math class="MJX-TEX" aria-hidden="true"><mjx-mi class="mjx-i"><mjx-c class="mjx-c1D443 TEX-I"></mjx-c></mjx-mi></mjx-math><mjx-assistive-mml unselectable="on" display="inline"><math xmlns="http://www.w3.org/1998/Math/MathML"><mi>P</mi></math></mjx-assistive-mml><span aria-hidden="true" class="no-mathjax mjx-copytext">$P$</span></mjx-container>을 <strong>포린드롬 수</strong>라고 정의한다.</li>
+</ul>
+
+<p>포닉스는 자신이 만든 수가 너무 아름답다고 느낀 나머지, 자신의 우월함을 뽐내기 위해 달구와 윤이에게 "주어진 <mjx-container class="MathJax" jax="CHTML" style="font-size: 104.6%; position: relative;"><mjx-math class="MJX-TEX" aria-hidden="true"><mjx-mi class="mjx-i"><mjx-c class="mjx-c1D441 TEX-I"></mjx-c></mjx-mi></mjx-math><mjx-assistive-mml unselectable="on" display="inline"><math xmlns="http://www.w3.org/1998/Math/MathML"><mi>N</mi></math></mjx-assistive-mml><span aria-hidden="true" class="no-mathjax mjx-copytext">$N$</span></mjx-container>에 대해, <mjx-container class="MathJax" jax="CHTML" style="font-size: 104.6%; position: relative;"><mjx-math class="MJX-TEX" aria-hidden="true"><mjx-mi class="mjx-i"><mjx-c class="mjx-c1D441 TEX-I"></mjx-c></mjx-mi></mjx-math><mjx-assistive-mml unselectable="on" display="inline"><math xmlns="http://www.w3.org/1998/Math/MathML"><mi>N</mi></math></mjx-assistive-mml><span aria-hidden="true" class="no-mathjax mjx-copytext">$N$</span></mjx-container>보다 작거나 같은 포린드롬 수의 개수를 구해봐!" 라고 문제를 냈다. 달구와 윤이를 도와 문제를 풀고, 포닉스의 코를 납작하게 해주자!</p>
+
+### 입력 
+
+ <p>첫 번째 줄에 <mjx-container class="MathJax" jax="CHTML" style="font-size: 104.6%; position: relative;"><mjx-math class="MJX-TEX" aria-hidden="true"><mjx-mi class="mjx-i"><mjx-c class="mjx-c1D441 TEX-I"></mjx-c></mjx-mi></mjx-math><mjx-assistive-mml unselectable="on" display="inline"><math xmlns="http://www.w3.org/1998/Math/MathML"><mi>N</mi></math></mjx-assistive-mml><span aria-hidden="true" class="no-mathjax mjx-copytext">$N$</span></mjx-container>의 값이 주어진다. <mjx-container class="MathJax" jax="CHTML" style="font-size: 104.6%; position: relative;"><mjx-math class="MJX-TEX" aria-hidden="true"><mjx-mo class="mjx-n"><mjx-c class="mjx-c28"></mjx-c></mjx-mo><mjx-mn class="mjx-n"><mjx-c class="mjx-c31"></mjx-c></mjx-mn><mjx-mo class="mjx-n" space="4"><mjx-c class="mjx-c2264"></mjx-c></mjx-mo><mjx-mi class="mjx-i" space="4"><mjx-c class="mjx-c1D441 TEX-I"></mjx-c></mjx-mi><mjx-mo class="mjx-n" space="4"><mjx-c class="mjx-c2264"></mjx-c></mjx-mo><mjx-msup space="4"><mjx-mn class="mjx-n"><mjx-c class="mjx-c31"></mjx-c><mjx-c class="mjx-c30"></mjx-c></mjx-mn><mjx-script style="vertical-align: 0.393em;"><mjx-texatom size="s" texclass="ORD"><mjx-mn class="mjx-n"><mjx-c class="mjx-c39"></mjx-c></mjx-mn></mjx-texatom></mjx-script></mjx-msup><mjx-mo class="mjx-n"><mjx-c class="mjx-c29"></mjx-c></mjx-mo></mjx-math><mjx-assistive-mml unselectable="on" display="inline"><math xmlns="http://www.w3.org/1998/Math/MathML"><mo stretchy="false">(</mo><mn>1</mn><mo>≤</mo><mi>N</mi><mo>≤</mo><msup><mn>10</mn><mrow data-mjx-texclass="ORD"><mn>9</mn></mrow></msup><mo stretchy="false">)</mo></math></mjx-assistive-mml><span aria-hidden="true" class="no-mathjax mjx-copytext">$(1 \le N \le 10^{9})$</span> </mjx-container></p>
+
+### 출력 
+
+ <p><mjx-container class="MathJax" jax="CHTML" style="font-size: 104.6%; position: relative;"> <mjx-math class="MJX-TEX" aria-hidden="true"><mjx-mi class="mjx-i"><mjx-c class="mjx-c1D441 TEX-I"></mjx-c></mjx-mi></mjx-math><mjx-assistive-mml unselectable="on" display="inline"><math xmlns="http://www.w3.org/1998/Math/MathML"><mi>N</mi></math></mjx-assistive-mml><span aria-hidden="true" class="no-mathjax mjx-copytext">$N$</span></mjx-container>보다 작거나 같은 포린드롬 수의 개수를 출력한다.</p>
+

백준/Silver/33690. 포린드롬/포린드롬.py

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+# 33690 포린드롬
+# 실버 5
+
+def is_palindrome(n):
+    s = str(n)
+    return s == s[::-1]
+
+def generate_palindromes(limit):
+    palindromes = []
+
+    # 홀수 길이 팰린드롬
+    for half in range(0, 100000):  # 최대 5자리까지
+        s = str(half)
+        p = int(s + s[-2::-1])  # 가운데 숫자 제외하고 뒤집기
+        if p > limit:
+            break
+        palindromes.append(p)
+
+    # 짝수 길이 팰린드롬
+    for half in range(1, 100000):  # 최대 5자리까지
+        s = str(half)
+        p = int(s + s[::-1])
+        if p > limit:
+            break
+        palindromes.append(p)
+
+    return palindromes
+
+def count_f(N):
+    result = 0
+    for p in generate_palindromes(N):
+        if is_palindrome(p // 10):
+            result += 1
+    return result
+
+if __name__ == "__main__":
+    import sys
+    input = sys.stdin.readline
+    N = int(input())
+    print(count_f(N))
+
+"""
+시간 초과
+
+import sys
+
+p = int(sys.stdin.readline())
+
+cnt = 0
+
+for n in range(0, p+1):
+    if len(set(list(str(n)))) == 1:
+        cnt += 1
+
+print(cnt)
+
+"""