codeforces#306 div2

第一次参加这个比赛

A：

#include <iostream>#include <string>using namespace std;int main(){string str = "";cin >> str;int m = 0, n = 0, i = 0;for (i = 0, m = 0, n = 0; i < str.size(); i++){if ((m == 0) && (str.at(i) == 'A')){if (i + 1 < str.size()){if (str.at(i + 1) == 'B'){i++;m = 1;continue;}}}if ((m != 0)&&(n == 0) && (str.at(i) == 'B')){if (i + 1 < str.size()){if (str.at(i + 1) == 'A'){i++;n = 1;}}}}if (m && n){cout << "YES";return 0;}for (i = 0, m = 0, n = 0; i < str.size(); i++){if ((m == 0) && (str.at(i) == 'B')){if (i + 1 < str.size()){if (str.at(i + 1) == 'A'){i++;m = 1;continue;}}}if ((m != 0) && (n == 0) && (str.at(i) == 'A')){if (i + 1 < str.size()){if (str.at(i + 1) == 'B'){i++;n = 1;}}}}if (m && n){cout << "YES";return 0;}cout << "NO";return 0;}

这一题一开始就想到了”ABAXXXAB“这样的测试点，写完代码后感觉自己完成了这个测试点

但是不知道怎么回事，最后发现还是个错的，最后修改了一点点，改对了

if ((m != 0) && (n == 0) && (str.at(i) == 'A'))

主要是这个里面加了一个

(m != 0)

B：

#include <iostream>#include <algorithm>typedef long long ll;using namespace std;int c[16] = { 0 };int s[16] = { 0 }; int n = 0, way = 0;ll l = 0, r = 0, x = 0;void judge(int s[], int j){int total = 0;if (s[j - 1] - s[0] < x) return;for (int i = 0; i < j; i++)total += s[i];if (total < l || total > r) return;way++;}void select(int i, int j)//j represent the length of s;{if (i == n){judge(s, j);return;}select(i + 1, j);s[j++] = c[i];select(i + 1, j);}int main(){int j = 0;cin >> n >> l >> r >> x;for (int i = 0; i <n; i++)cin >> c[i];//0~n-1sort(c, c + n);select(0, j);cout << way << endl;}

这一题是赛后做出来的，本来就想到了用二进制进行移位，最后还是没有用

   for(int i=0; i<(1<<n); i++){

    for(int j=0; j<15; j++){
                        if( (i>>j)&1 ){

可以这样用

C：暴力求解

#include <iostream>#include <string>using namespace std;int main(){string str = "";cin >> str;int num = 0;for (int i = 0; i < str.size(); i++){if (str.at(i) == '0'){cout << "YES" << endl;cout << "0";return 0;}if (str.at(i) == '8'){cout << "YES" << endl;cout << "8";return 0;}}for (int i = 0; i < str.size(); i++){for (int j = i + 1; j < str.size(); j++){num = (str.at(i) - '0') * 10 + (str.at(j) - '0');if (num % 8 == 0){cout << "YES" << endl;cout << num;return 0;}}}for (int i = 0; i < str.size(); i++){for (int j = i + 1; j < str.size(); j++){for (int k = j + 1; k < str.size(); k++){num = (str.at(i) - '0') * 100 + (str.at(j) - '0') * 10 + (str.at(k) - '0');if (num % 8 == 0){cout << "YES" << endl;cout << num;return 0;}}}}cout << "NO";return 0;}

D：

#include <iostream>using namespace std;int main(){int k = 0;int n = 0, m = 0, h = 0;int v1 = 0, v2 = 0;cin >> k;if ((k % 2) == 0){cout << "NO";return 0;}cout << "YES" << endl;n = 4 * k - 2;h = 2 * k * k - k;m = k;cout << n << " " << h << endl;for (int i = 1; i < m; i++){v1 = 1;v2 = i + 1;cout << v1 << " " << v2 << endl;}// first verticefor (int i = 2; i <= m; i++){for (int j = m + 1; j <= 2*m - 1; j++){v1 = i;v2 = j;cout << v1 << " " << v2 << endl;}}//2~m verticefor (int i = m + 1; i <= 2*m - 1; i = i + 2){v1 = i;v2 = i + 1;cout << v1 << " " << v2 << endl;}int app = 2*m - 1;v1 = 1;v2 = 1 + app;cout << v1 << " " << v2 << endl;for (int i = 1 + app; i < m + app; i++){v1 = 1 + app;v2 = i + 1;cout << v1 << " " << v2 << endl;}for (int i = 2 + app; i <= m + app; i++){for (int j = m + 1 + app; j <= 2*m - 1 + app; j++){v1 = i;v2 = j;cout << v1 << " " << v2 << endl;}}for (int i = m + 1 + app; i <= 2*m - 1 + app; i = i + 2){v1 = i;v2 = i + 1;cout << v1 << " " << v2 << endl;}}

这一题开始时推导用了好久，得出结论k必需为一个奇数，之后级还好 了

这一题期望看到他人的思路

E：

#include <iostream>#define maxn 100000 + 10using namespace std;int n;int a[maxn] = { 0 };int main(){int flag = 0;cin >> n;for (int i = 0; i < n; i++) cin >> a[i];if (n == 1){ cout << "YES" << endl; cout << a[0]; return 0; }if (a[n - 1] != 0){ cout << "NO"; return 0; }for (int i = 0; i < n - 2; i++) if (a[i] != 1) { flag = 1; break; }if (flag == 0 && a[n - 2] == 0){ cout << "NO"; return 0; }cout << "YES" << endl;cout << "(";for (int i = 0; i < n-1; i++){if (a[i] == 1)cout << "1->";elsecout << "0)->(";}cout << "0)" << endl;return 0;}

这一题自认为是正确的，不知是不是题意理解有问题，没有过

有许多总结之处：

感觉用时太长了，一题要做半个小时都不止