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UVA 12206 - Stammering Aliens(后缀数组)
UVA 12206 - Stammering Aliens
题目链接
题意:给定一个序列,求出出现次数大于m,长度最长的子串的最大下标
思路:后缀数组,搞出height数组后,利用二分去查找即可
这题之前还写过hash的写法也能过,不过写后缀数组的时候,犯了一个傻逼错误,把none输出成node还一直找不到。。。这是刷题来第二次碰到这种逗比错误了,还是得注意。。
代码:
#include <cstdio> #include <cstring> #include <algorithm> using namespace std; const int MAXLEN = 40005; struct Suffix { int s[MAXLEN]; int sa[MAXLEN], t[MAXLEN], t2[MAXLEN], c[MAXLEN], n; int rank[MAXLEN], height[MAXLEN]; void build_sa(int m) { n++; int i, *x = t, *y = t2; for (i = 0; i < m; i++) c[i] = 0; for (i = 0; i < n; i++) c[x[i] = s[i]]++; for (i = 1; i < m; i++) c[i] += c[i - 1]; for (i = n - 1; i >= 0; i--) sa[--c[x[i]]] = i; for (int k = 1; k <= n; k <<= 1) { int p = 0; for (i = n - k; i < n; i++) y[p++] = i; for (i = 0; i < n; i++) if (sa[i] >= k) y[p++] = sa[i] - k; for (i = 0; i < m; i++) c[i] = 0; for (i = 0; i < n; i++) c[x[y[i]]]++; for (i = 0; i < m; i++) c[i] += c[i - 1]; for (i = n - 1; i >= 0; i--) sa[--c[x[y[i]]]] = y[i]; swap(x, y); p = 1; x[sa[0]] = 0; for (i = 1; i < n; i++) x[sa[i]] = (y[sa[i - 1]] == y[sa[i]] && y[sa[i - 1] + k] == y[sa[i] + k]) ? p - 1 : p++; if (p >= n) break; m = p; } n--; } void getHeight() { int i, j, k = 0; for (i = 1; i <= n; i++) rank[sa[i]] = i; for (i = 0; i < n; i++) { if (k) k--; int j = sa[rank[i] - 1]; while (s[i + k] == s[j + k]) k++; height[rank[i]] = k; } } } gao; const int N = 40005; int m; char str[N]; int judge(int x) { int ans = -1; for (int i = 1; i <= gao.n; i++) { if (gao.n - gao.sa[i] < x) continue; int Max = gao.sa[i], cnt = 1; while (gao.height[i + 1] >= x && i < gao.n) { Max = max(Max, gao.sa[i + 1]); cnt++; i++; } if (cnt >= m) ans = max(ans, Max); } return ans; } void solve() { if (judge(1) == -1) { printf("none\n"); return; } int l = 1, r = gao.n - m + 2; while (l < r) { int mid = (l + r) / 2; if (judge(mid) != -1) l = mid + 1; else r = mid; } l--; printf("%d %d\n", l, judge(l)); } int main() { while (~scanf("%d", &m) && m) { scanf("%s", str); int len = strlen(str); for (int i = 0; i < len; i++) gao.s[i] = str[i] - 'a' + 1; gao.s[len] = 0; gao.n = len; gao.build_sa(27); gao.getHeight(); solve(); } return 0; }
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