From 031a698ef591fed9958d2ca31c2f20ddec86a516 Mon Sep 17 00:00:00 2001
From: Ariel <ariel@arielherself.xyz>
Date: Sat, 20 Jan 2024 15:09:34 +0800
Subject: [PATCH] Create sa.cc

---
 string/sa.cc | 49 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 49 insertions(+)
 create mode 100644 string/sa.cc

diff --git a/string/sa.cc b/string/sa.cc
new file mode 100644
index 0000000..b8165ef
--- /dev/null
+++ b/string/sa.cc
@@ -0,0 +1,49 @@
+#include <algorithm>
+#include <cstdio>
+#include <cstring>
+#include <iostream>
+
+using namespace std;
+
+const int N = 1000010;
+
+char s[N];
+// key1[i] = rk[id[i]]（作为基数排序的第一关键字数组）
+int n, sa[N], rk[N], oldrk[N << 1], id[N], key1[N], cnt[N];
+
+bool cmp(int x, int y, int w) {
+  return oldrk[x] == oldrk[y] && oldrk[x + w] == oldrk[y + w];
+}
+
+int main() {
+  int i, m = 127, p, w;
+
+  scanf("%s", s + 1);
+  n = strlen(s + 1);
+  for (i = 1; i <= n; ++i) ++cnt[rk[i] = s[i]];
+  for (i = 1; i <= m; ++i) cnt[i] += cnt[i - 1];
+  for (i = n; i >= 1; --i) sa[cnt[rk[i]]--] = i;
+
+  for (w = 1;; w <<= 1, m = p) {  // m=p 就是优化计数排序值域
+    for (p = 0, i = n; i > n - w; --i) id[++p] = i;
+    for (i = 1; i <= n; ++i)
+      if (sa[i] > w) id[++p] = sa[i] - w;
+
+    memset(cnt, 0, sizeof(cnt));
+    for (i = 1; i <= n; ++i) ++cnt[key1[i] = rk[id[i]]];
+    // 注意这里px[i] != i，因为rk没有更新，是上一轮的排名数组
+
+    for (i = 1; i <= m; ++i) cnt[i] += cnt[i - 1];
+    for (i = n; i >= 1; --i) sa[cnt[key1[i]]--] = id[i];
+    memcpy(oldrk + 1, rk + 1, n * sizeof(int));
+    for (p = 0, i = 1; i <= n; ++i)
+      rk[sa[i]] = cmp(sa[i], sa[i - 1], w) ? p : ++p;
+    if (p == n) {
+      break;
+    }
+  }
+
+  for (i = 1; i <= n; ++i) printf("%d ", sa[i]);
+
+  return 0;
+}