Codeforces Round #352 (Div. 2)
#include <bits/stdc++.h> int a[1100]; int b[100]; int len; void init() { int i = 1, tot = 1; while (tot <= 1010) { int t = i, c = 0; while (t) { b[c++] = t % 10; t /= 10; } for (int i=c-1; i>=0; --i) { a[tot++] = b[i]; } i++; } } int main() { init (); int n; scanf ("%d", &n); printf ("%d", a[n]); return 0; }
题意:问最少改变多少个字母使得该字符串的所有子串不相同
分析:子串有长度为1的,所以如果字符串长度大于26一定不可行,否则就把相同的字母用没出现的字母替换.
#include <bits/stdc++.h> const int N = 1e5 + 5; char str[N]; int vis[30]; int main() { int n; scanf ("%d%s", &n, str); if (n > 26) { puts ("-1"); } else { int ans = 0; for (int i=0; i<n; ++i) { if (vis[str[i]-'a']) { ans++; } else { vis[str[i]-'a'] = true; } } printf ("%d\n", ans); } return 0; }
几何+贪心 C - Recycling Bottles
题意:A和B捡罐头,每次只能捡一个然后到垃圾桶去,再从垃圾桶出发去捡,问捡完所有罐头所需的最少总路程
分析:除从A或B出发第一次捡罐头的距离不确定外,其他的都可以看成sum (dis (T, p[i]) *2),所以只需要 min (-dis (T, p[i]) + dis (A, p[i])).因为A和B捡罐头是独立的,只要A和B都捡一个罐头使得差值最小,重复时特判下就行了.更一般的做法是A任意选择一个罐头,B选择除A选的外里最小差值的那一个,可以预处理出前缀最小和后缀最小.
#include <bits/stdc++.h> const int N = 1e5 + 5; const double INF = 1e18 + 5; const double EPS = 1e-8; struct Point { double x, y; Point() {} Point(double x, double y) { this->x = x; this->y = y; } }point[N]; Point A, B, O; double dis[N]; double sum; double pre[N], suff[N]; double add[N]; int n; Point read_point() { double x, y; scanf ("%lf%lf", &x, &y); return Point (x, y); } double squ(double x) { return x * x; } double calc_dis(Point a, Point b) { return sqrt (squ (a.x - b.x) + squ (a.y - b.y)); } int main() { A = read_point (); B = read_point (); O = read_point (); scanf ("%d", &n); for (int i=1; i<=n; ++i) { point[i] = read_point (); dis[i] = calc_dis (point[i], O); pre[i] = suff[i] = -dis[i] + calc_dis (point[i], B); add[i] = -dis[i] + calc_dis (point[i], A); sum += dis[i] * 2; } pre[0] = suff[n+1] = INF; for (int i=1; i<=n; ++i) { pre[i] = std::min (pre[i], pre[i-1]); } for (int i=n; i>=1; --i) { suff[i] = std::min (suff[i], suff[i+1]); } double ans = sum + suff[1]; //just B for (int i=1; i<=n; ++i) { ans = std::min (ans, sum + std::min (0.0, std::min (pre[i-1], suff[i+1])) + add[i]); } printf ("%.12f\n", ans); return 0; }
题意:n个人,k次操作,每次把最大的数分1到最小的数,问k次后最大值和最小值的差
分析:二分最小值和最大值,思想是求出min(max) 刚好使得小于它的到它的操作正好是k.处理好二分的边界,因为二分时是尽量使得最小值大,最大值小.
#include <bits/stdc++.h> typedef long long ll; const int N = 5e5 + 5; int a[N]; int n, k; bool check(int val, int op) { ll need = 0; for (int i=0; i<n; ++i) { if (op == 1) { if (a[i] <= val) { need += val - a[i]; } else { break; } } else if (op == 2 && a[i] >= val) { need += a[i] - val; } } return need <= k; } int main() { scanf ("%d%d", &n, &k); ll sum = 0; for (int i=0; i<n; ++i) { scanf ("%d", a+i); sum += a[i]; } std::sort (a, a+n); int ansl = -1, ansr = 1e9; int left = a[0], right = sum / n; while (left <= right) { int mid = left + (right - left) / 2; if (check (mid, 1)) { ansl = mid; left = mid + 1; } else { right = mid - 1; } } left = sum / n; if (sum % n) { left++; } right = a[n-1]; while (left <= right) { int mid = left + (right - left) / 2; if (check (mid, 2)) { ansr = mid; right = mid - 1; } else { left = mid + 1; } } printf ("%d\n", ansr - ansl); return 0; }
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