题目描述
FJ is about to take his N (1 ≤ N ≤ 30,000) cows to the annual"Farmer of the Year" competition. In this contest every farmer arranges his cows in a line and herds them past the judges.
The contest organizers adopted a new registration scheme this year: simply register the initial letter of every cow in the order they will appear (i.e., If FJ takes Bessie, Sylvia, and Dora in that order he just registers BSD). After the registration phase ends, every group is judged in increasing lexicographic order according to the string of the initials of the cows' names.
FJ is very busy this year and has to hurry back to his farm, so he wants to be judged as early as possible. He decides to rearrange his cows, who have already lined up, before registering them.
FJ marks a location for a new line of the competing cows. He then proceeds to marshal the cows from the old line to the new one by repeatedly sending either the first or last cow in the (remainder of the) original line to the end of the new line. When he's finished, FJ takes his cows for registration in this new order.
Given the initial order of his cows, determine the least lexicographic string of initials he can make this way.
每次只能从两边取，要求取出来之后字典序最小
输入输出格式
输入格式：-
Line 1: A single integer: N
- Lines 2..N+1: Line i+1 contains a single initial ('A'..'Z') of the cow in the ith position in the original line
The least lexicographic string he can make. Every line (except perhaps the last one) contains the initials of 80 cows ('A'..'Z') in the new line.
输入输出样例
6 A C D B C B
ABCBCD
【题解】
贪心即可。
正解sa，但我暴力了，留着以后学了sa再写
1 #include <iostream> 2 #include <cstdio> 3 #include <cstdlib> 4 #include <cstring> 5 6 const int INF = 0X3f3f3f3f; 7 const int MAXN = 3000000 + 10; 8 9 char s[MAXN]; 10 int n, cnt; 11 12 int main() 13 { 14 scanf("%d", &n);char ch; 15 for(register int i = 1;i <= n;++ i) 16 { 17 ch = getchar(); 18 while(ch < 'A' || ch > 'Z')ch = getchar(); 19 s[i] = ch; 20 } 21 int l = 1, r = n; 22 while(l < r - 1) 23 { 24 if(s[l] < s[r]) 25 { 26 printf("%c", s[l]), ++ l; 27 ++ cnt; 28 if(cnt == 80) 29 { 30 printf(" "); 31 cnt = 0; 32 } 33 } 34 else if(s[l] > s[r]) 35 { 36 printf("%c", s[r]), -- r; 37 ++ cnt; 38 if(cnt == 80) 39 { 40 printf(" "); 41 cnt = 0; 42 } 43 } 44 else 45 { 46 int p = l, q = r; 47 while(p < q - 1 && s[p] == s[q])++ p, -- q; 48 if(( p == q) || (p == q - 1 && s[p] == s[q]) ) 49 { 50 char ch = s[l]; 51 for(;l < p && s[l] == ch;++ l) 52 { 53 printf("%c", s[l]); 54 ++ cnt; 55 if(cnt == 80) 56 { 57 printf(" "); 58 cnt = 0; 59 } 60 } 61 } 62 else if(s[p] < s[q]) 63 { 64 char ch = s[l]; 65 for(;l < p && s[l] == ch;++ l) 66 { 67 printf("%c", s[l]); 68 ++ cnt; 69 if(cnt == 80) 70 { 71 printf(" "); 72 cnt = 0; 73 } 74 } 75 } 76 else if(s[p] > s[q]) 77 { 78 char ch = s[r]; 79 for(;r > q && s[r] == ch;-- r) 80 { 81 printf("%c", s[r]); 82 ++ cnt; 83 if(cnt == 80) 84 { 85 printf(" "); 86 cnt = 0; 87 } 88 } 89 } 90 } 91 } 92 if(l == r)printf("%c", s[l]); 93 else if(s[l] < s[r]) 94 { 95 printf("%c", s[l]); 96 ++ cnt; 97 if(cnt == 80) 98 { 99 printf(" "); 100 cnt = 0; 101 } 102 printf("%c", s[r]); 103 } 104 else 105 { 106 printf("%c", s[r]); 107 ++ cnt; 108 if(cnt == 80) 109 { 110 printf(" "); 111 cnt = 0; 112 } 113 printf("%c", s[l]); 114 } 115 return 0; 116 }