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Description
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:
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.
A 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.
In a single line print the required string. If there isn‘t such string, print "-1" (without the quotes).
7 4
ababacd
4 7
-1
正解：贪心
解题报告：
直接每次贪心地让ab不断重复，注意特判一些细节，这题的数据好坑
1 //It is made by jump~ 2 #include <iostream> 3 #include <cstdlib> 4 #include <cstring> 5 #include <cstdio> 6 #include <cmath> 7 #include <algorithm> 8 #include <ctime> 9 #include <vector> 10 #include <queue> 11 #include <map> 12 #include <set> 13 using namespace std; 14 typedef long long LL; 15 int n,k,cnt; 16 17 inline int getint() 18 { 19 int w=0,q=0; char c=getchar(); 20 while((c<‘0‘ || c>‘9‘) && c!=‘-‘) c=getchar(); if(c==‘-‘) q=1,c=getchar(); 21 while (c>=‘0‘ && c<=‘9‘) w=w*10+c-‘0‘, c=getchar(); return q ? -w : w; 22 } 23 24 inline void work(){ 25 n=getint(); k=getint(); 26 if(k>n || (k==1 && n>1)) { printf("-1"); return ; } 27 if(k==1 && n==1) { printf("a"); return ; } 28 cnt=2; k-=2; 29 for(int i=1;i<=n;i++) { 30 if(n-i<k) printf("%c",(char)cnt+‘a‘),cnt++; 31 else { 32 if(i&1) printf("a"); else printf("b"); 33 } 34 } 35 } 36 37 int main() 38 { 39 work(); 40 return 0; 41 }
codeforces 288A：Polo the Penguin and Strings
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原文地址：http://www.cnblogs.com/ljh2000-jump/p/5885907.html
