ZOJ3171 The Hidden 7's,DP版
2011-09-13 12:54
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这题算是非典型的DP 吧。可以看一下代码中的注释。
/******************************************************************************* # Author : Neo Fung # Email : neosfung@gmail.com # Last modified: 2011-09-13 12:53 # Filename: ZOJ3171 The Hidden 7's.cpp # Description : ******************************************************************************/ // ZOJ3171 The Hidden 7's.cpp : Defines the entry point for the console application. // // #include "stdafx.h" // #define DEBUG #include <fstream> #include <stdio.h> #include <iostream> #include <string.h> #include <string> #include <memory.h> using namespace std; int main(void) { #ifdef DEBUG freopen("data.txt","r",stdin); #endif char seven[]=" seven"; char str[10010]; long long unsigned dp[6]; while(gets(str) && strlen(str)) { memset(dp,0,sizeof(dp)); dp[0]=1; for(int i=0;str[i];++i) { if (str[i]>='A' && str[i]<='Z') { str[i]+='a'-'A'; } for(int j=5;j>0;--j) if(str[i]==seven[j]) //dp[j]表示到达seven[j]有多少条路径。如果str[i]和seven[j]相等,则dp[j]就多出dp[j-1]条路径。类似于01背包,因为str中的每个字符只能取一次,所以要从后往前遍历。 dp[j]=dp[j-1]+dp[j]; } printf("%llu\n",dp[5]); } return 0; }
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