题意:给定一个序列,让你找出一个最长的序列,使得最多改其中的一个数,使其变成严格上升序列。
析:f[i] 表示以 i 结尾的最长上升长度,g[i] 表示以 i 为开始的最长上升长度,这两个很容易就求得,最后枚举中间值即可。
代码如下:
#pragma comment(linker, "/STACK:1024000000,1024000000") #include <cstdio> #include <string> #include <cstdlib> #include <cmath> #include <iostream> #include <cstring> #include <set> #include <queue> #include <algorithm> #include <vector> #include <map> #include <cctype> #include <cmath> #include <stack> #define lson l,m,rt<<1 #define rson m+1,r,rt<<1|1 //#include <tr1/unordered_map> #define freopenr freopen("in.txt", "r", stdin) #define freopenw freopen("out.txt", "w", stdout) using namespace std; //using namespace std :: tr1; typedef long long LL; typedef pair<int, int> P; const int INF = 0x3f3f3f3f; const double inf = 0x3f3f3f3f3f3f; const LL LNF = 0x3f3f3f3f3f3f; const double PI = acos(-1.0); const double eps = 1e-8; const int maxn = 1e5 + 5; const LL mod = 10000000000007; const int N = 1e6 + 5; const int dr[] = {-1, 0, 1, 0, 1, 1, -1, -1}; const int dc[] = {0, 1, 0, -1, 1, -1, 1, -1}; const char *Hex[] = {"0000", "0001", "0010", "0011", "0100", "0101", "0110", "0111", "1000", "1001", "1010", "1011", "1100", "1101", "1110", "1111"}; inline LL gcd(LL a, LL b){ return b == 0 ? a : gcd(b, a%b); } int n, m; const int mon[] = {0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}; const int monn[] = {0, 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}; inline int Min(int a, int b){ return a < b ? a : b; } inline int Max(int a, int b){ return a > b ? a : b; } inline LL Min(LL a, LL b){ return a < b ? a : b; } inline LL Max(LL a, LL b){ return a > b ? a : b; } inline bool is_in(int r, int c){ return r >= 0 && r < n && c >= 0 && c < m; } int f[maxn], g[maxn], a[maxn]; int main(){ while(scanf("%d", &n) == 1){ a[0] = 0; memset(f, 0, sizeof f); memset(g, 0, sizeof g); for(int i = 1; i <= n; ++i) scanf("%d", a+i); f[0] = 0; f[1] = 1; for(int i = 2; i <= n; ++i) if(a[i] > a[i-1]) f[i] = f[i-1] + 1; else f[i] = 1; g[n] = 1; for(int i = n-1; i > 0; --i) if(a[i] < a[i+1]) g[i] = g[i+1] + 1; else g[i] = 1; int ans = 0; for(int i = 1; i <= n; ++i){ ans = Max(ans, f[i]+g[i]-1); if(i < n) ans = Max(ans, f[i]+1); if(i > 1) ans = Max(ans, g[i]+1); if(i > 1 && a[i] > a[i-1]) ans = Max(ans, f[i-1]+g[i]); if(i < n && a[i] < a[i+1]) ans = Max(ans, f[i]+g[i+1]); if(i > 1 && i < n && a[i+1] - a[i-1] > 1) ans = Max(ans, f[i-1]+g[i+1]+1); } printf("%d\n", ans); } return 0; }
时间: 2024-10-25 21:33:53