Codeforces Round #FF (Div. 2) C. DZY Loves Sequences
2017-08-07 10:40
537 查看
题目链接
http://codeforces.com/problemset/problem/447/C题目大意
给你n个数, 可以改变一个数值, 问你最长严格递增序列的长度思路
这题的意思很明确, 但是如何实现以及细节处理上存在很大问题首先实现上, 如果只用一个数组去模拟这个过程求最大值,很容易写挫且会有bug
我们先不考虑修改一个数, 从前往后用up[i]记录第i个位置上升序列的长度,从后往前用dw[i]记录第i个位置下降序列的长度
这样考虑修改一个数之后 ans = max(ans, up[i] + dw[i] + 1)
细节方面, 只有num[i] + 1 < num[i+2] 才能修改num[i+1]
还有就是ans 还可以 = max(ans, max(up[i] + 1, dw[i] + 1)), 也就是在最长序列头或者尾修改一个数, 这时要小心一个bug, 就是n个数都递增时, ans可能>n, 这显然是错的, 要特判一下
代码
#include<bits/stdc++.h> using namespace std; const int M = 1e6 + 5; int num[M], up[M], dw[M]; int main() { int n; memset(up, 0, sizeof(up)); memset(dw, 0, sizeof(dw)); scanf("%d", &n); for(int i=0; i<n; ++i) scanf("%d", num+i); int tot = 1; up[0] = 1, dw[n-1] = 1; for(int i=1; i<n; ++i) { if(num[i] > num[i-1]) ++tot; else tot = 1; up[i] = tot; } tot = 1; for(int i=n-2; i>=0; --i) { if(num[i] < num[i+1]) ++tot; else tot = 1; dw[i] = tot; } int ans = 1; for(int i=0; i<n-2; ++i) { if(num[i] + 1 < num[i+2]) ans = max(ans, up[i] + dw[i+2] + 1); } for(int i=0; i<n; ++i) ans = max(ans, max(up[i]+1, dw[i]+1)); if(ans > n) ans = n; printf("%d\n", ans); return 0; }
反思
代码实现能力太差了, 集训半个月前一路wa过去, 现在还是一路wa过去。。。orz相关文章推荐
- Codeforces Round #FF (Div. 2/C)/Codeforces446A_DZY Loves Sequences(DP)
- Codeforces Round #FF (Div. 2)-C. DZY Loves Sequences
- Codeforces Round #FF (Div. 2) C DZY Loves Sequences
- DP Codeforces Round #FF (Div. 1) A. DZY Loves Sequences
- Codeforces Round #FF (Div. 1) A. DZY Loves Sequences 动态规划
- Codeforces Round #FF (Div. 2) C. DZY Loves Sequences
- Codeforces Round #FF (Div. 二):C. DZY Loves Sequences
- Codeforces Round #FF (Div. 2):C. DZY Loves Sequences
- Codeforces Round #FF (Div. 2)446A - DZY Loves Sequences(最长上升子序列变形)
- Codeforces Round #FF (Div. 2):C. DZY Loves Sequences
- Codeforces Round #FF (Div. 2) C - DZY Loves Sequences (DP)
- Codeforces Round #FF (Div. 2)C. DZY Loves Sequences
- Codeforces Round #FF (Div. 1) A. DZY Loves Sequences 动态规划
- Codeforces Round #FF (Div. 1) A. DZY Loves Sequences
- Codeforces Round #FF (Div. 2) Problem C DZY Loves Sequences
- Codeforces Round #FF (Div. 2) C. DZY Loves Sequences
- Codeforces Round #FF (Div. 2)C. DZY Loves Sequences
- Codeforces Round #FF (Div. 2)C - DZY Loves Sequences
- Codeforces Round #FF (Div. 2) C. DZY Loves Sequences
- Codeforces Round #FF (Div. 2)-C. DZY Loves Sequences