题目链接：http://codeforces.com/contest/1157/problem/C2
当左右两边数字相同时，需要判断一下取哪边能得到更长的递增序列
#include <iostream> #include <cstring> #include <algorithm> #include <cmath> #include <cstdio> #include <queue> #include <climits> #include <set> #include <stack> #include <string> #include <map> #include <vector> #define INF 0x3f3f3f3f using namespace std; typedef long long ll; static const int MAX_N = 2e5 + 5; static const ll Mod = 2009; char str[MAX_N]; int a[MAX_N]; void solve(){ // freopen("input.txt", "r", stdin); // freopen("output.txt", "w", stdout); int n; while(scanf("%d", &n) != EOF){ for(int i = 0; i < n; ++i) scanf("%d", &a[i]); int s = 0, e = n - 1, cnt = 0, prev = 0; //prev为序列中最大值 while(s <= e){ if(a[s] <= prev){ while(a[e] > prev && e >= s){ prev = a[e--]; str[cnt++] = 'R'; } break; } if(a[e] <= prev){ while(a[s] > prev && s <= e){ prev = a[s++]; str[cnt++] = 'L'; } break; } if(a[s] < a[e] && a[s] > prev){ prev = a[s++]; str[cnt++] = 'L'; continue; } if(a[s] > a[e] && a[e] > prev){ prev = a[e--]; str[cnt++] = 'R'; continue; } int e1 = 0, e2 = 0; if(a[s] > prev){ e1 = 1; while(s + e1 <= e && a[s + e1] > a[s + e1 - 1]) ++e1; } if(a[e] > prev){ e2 = 1; while(e - e2 >= s && a[e - e2] > a[e - e2 + 1]) ++e2; } if(e1 > e2){ prev = a[s++]; str[cnt++] = 'L'; } else{ prev = a[e--]; str[cnt++] = 'R'; } } str[cnt] = '\0'; printf("%d\n%s\n", cnt, str); } } int main() { solve(); return 0; }