HDOJ(HDU).2266 How Many Equations Can You Find (DFS)

HDOJ(HDU).2266 How Many Equations Can You Find (DFS) [从零开始DFS(9)]

点我挑战题目

从零开始DFS
HDOJ.1342 Lotto [从零开始DFS(0)] — DFS思想与框架/双重DFS
HDOJ.1010 Tempter of the Bone [从零开始DFS(1)] —DFS四向搜索/奇偶剪枝
HDOJ(HDU).1015 Safecracker [从零开始DFS(2)] —DFS四向搜索变种
HDOJ(HDU).1016 Prime Ring Problem (DFS) [从零开始DFS(3)] —小结：做DFS题目的关注点
HDOJ(HDU).1035 Robot Motion [从零开始DFS(4)]—DFS题目练习
HDOJ(HDU).1241 Oil Deposits(DFS) [从零开始DFS(5)] —DFS八向搜索/双重for循环遍历
HDOJ(HDU).1258 Sum It Up (DFS) [从零开始DFS(6)] —DFS双重搜索/去重技巧
HDOJ(HDU).1045 Fire Net [从零开始DFS(７)]—DFS练习/check函数的思想
POJ.1416 Shredding Company [从零开始DFS(8)]—DFS练习/sum函数的设计
HDOJ(HDU).2266 How Many Equations Can You Find (DFS) [从零开始DFS(9)]—DFS练习

题意分析

和POJ.1416 Shredding Company [从零开始DFS(8)]一模一样，简直了！

唯一需要注意的就是有可能不是求和，而是做减法。于是又多了一层dfs。当gap[i] = 2的时候代表做减法。求和的时候相减就行了。上代码上代码，快哉！

代码总览

/*    Title:HDOJ.2266    Author:pengwill    Date:2017-2-14*/#include <iostream>#include <cstdio>#include <cstring>#include <algorithm>using namespace std;char nu[100];int num[100],gap[100],save[100];int ret,len,test,time= 0;long long tar;void init(){    memset(gap,0,sizeof(gap));    len = strlen(nu);    for(int i = 0,j = 1; i<len;++i,++j) num[j] = nu[i]-'0';    ret = 0;gap[0] = gap[len] = 1; test = 0;time = 0;}int sum(){    int base = 1; int ans = 0; int t = 0;    for(int i = len ; i>=0; --i){        if(gap[i] == 0){            base*=10;            t += num[i] * base;        }else if(gap[i] == 1){            ans+=t; base = 1;            t = num[i] * base;        }else if(gap[i] == 2){            ans-=t; base = 1;            t = num[i] * base;        }    }    return ans;}void cpy(){    for(int i = 0; i<=len ;++i) save[i] = gap[i];}void output(){    for(int i = 1;i<=len;++i){        printf("%d",num[i]);        if(i!=len){            if(save[i] == 1) printf(" ");        }    }    printf("\n");}void dfs(int depth,int tag){    if(len==depth){        int t = sum();        if(t == tar) ret++;        return;    }    gap[depth] = tag;    if(depth == len-1){        dfs(depth+1,1);//chose gap    }else{        dfs(depth+1,1);//chose gap +        dfs(depth+1,0);//don't chose gap        dfs(depth+1,2);//chose gap -    }}int main(){    //freopen("in.txt","r",stdin);    while(scanf("%s %lld",&nu,&tar)!= EOF){        init();        dfs(0,1);        printf("%d\n",ret);    }    return 0;}