A. Polo the Penguin and Strings
Little penguin Polo adores strings. But most of all he adores strings of length n.
One day he wanted to find a string that meets the following conditions:
- The string consists of n lowercase English letters (that is, the string's length equals n), exactly k of these letters are distinct.
- No two neighbouring letters of a string coincide; that is, if we represent a string as s = s1s2... sn, then the following inequality holds,si ≠ si + 1(1 ≤ i < n).
- Among all strings that meet points 1 and 2, the required string is lexicographically smallest.
Help him find such string or state that such string doesn't exist.
String x = x1x2... xp is lexicographically less than string y = y1y2... yq, if either p < q and x1 = y1, x2 = y2, ... , xp = yp, or there is such number r (r < p, r < q), that x1 = y1, x2 = y2, ... , xr = yr and xr + 1 < yr + 1. The characters of the strings are compared by their ASCII codes.
InputA single line contains two positive integers n and k (1 ≤ n ≤ 106, 1 ≤ k ≤ 26) — the string's length and the number of distinct letters.
OutputIn a single line print the required string. If there isn't such string, print "-1" (without the quotes).
Sample test(s) input7 4output
ababacdinput
4 7output
-1
解题说明:此题是一道典型的贪心问题。既要保证字符串中随意两个连续字符串不同。也要保证字典序最小。最简单的想法是仅仅用a,b交替,在最后补上其它字符串就可以。
#include<iostream> #include<cstdio> #include<cmath> #include<cstdlib> #include <algorithm> #include<cstring> #include<string> using namespace std; int main() { int n, k, c, r, i; scanf("%d%d", &n, &k); if (k == n&&k <= 26) { c = 'a'; for (i = 0; i<k; i++) { printf("%c", c + i); } printf("\n"); } else if (k>n || k == 1) { printf("-1\n"); } else { for (i = 0; i<n - (k - 2); i++) { if (i % 2 == 0) { printf("a"); } else { printf("b"); } } r = 2; c = 'a'; for (i; i < n; i++, r++) { printf("%c", c + r); } printf("\n"); } return 0; }
- A. Polo the Penguin and Strings
- CUIT ACM Personal Training 11.27(FM)F - Polo the Penguin and Strings
- A. Polo the Penguin and Strings
- Codeforces Round #177 (Div. 1) A - Polo the Penguin and Strings
- codeforces 288A:Polo the Penguin and Strings
- CodeForces 288C Polo the Penguin and XOR operation (位运算,异或)
- Codeforces Round #177 (Div. 1) C. Polo the Penguin and XOR operation(贪心)
- codeforces 289 B. Polo the Penguin and Matrix
- codeforces 289 B. Polo the Penguin and Matrix
- B. Polo the Penguin and Matrix
- codechef Polo the Penguin and the Tree
- codeforces#289_B Polo the Penguin and Matrix
- Codeforces Round #177 (Div. 2)---E. Polo the Penguin and XOR operation(贪心)
- codeforces#289_B Polo the Penguin and Matrix
- CF_288B_PoloThePenguinAndHouses
- Codeforces Round #177 (Div. 1)C. Polo the Penguin and XOR operation【贪心】
- CF 288C (Polo the Penguin and XOR operation)
- CodeForces 289A Polo the Penguin and Segments
- codeforces 289B - Polo the Penguin and Matrix 二分+dp
- Codeforces-289a I Polo the Penguin and Segments