edit ch6+7 code

stevenhalim · Jun 30, 2020 · d655ea6 · d655ea6
1 parent 0386545
commit d655ea6
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Showing 8 changed files with 819 additions and 10 deletions.
diff --git a/ch6/sa_lcp.cpp b/ch6/sa_lcp.cpp
@@ -53,7 +53,7 @@ class SuffixArray {
     for (int i = 0, L = 0; i < n; ++i) {         // compute PLCP in O(n)
       if (Phi[i] == -1) { PLCP[i] = 0; continue; } // special case
       while ((i+L < n) && (Phi[i]+L < n) && (T[i+L] == T[Phi[i]+L]))
-        L++;                                     // L incr max n times
+        ++L;                                     // L incr max n times
       PLCP[i] = L;
       L = max(L-1, 0);                           // L dec max n times
     }
@@ -114,7 +114,7 @@ class SuffixArray {
   }
 };
 
-const int MAX_N = 200010;                        // can go up to 400K chars
+const int MAX_N = 450010;                        // can go up to 450K chars
 
 char T[MAX_N];
 char P[MAX_N];

diff --git a/ch6/sa_lcp_slow.cpp b/ch6/sa_lcp_slow.cpp
@@ -18,13 +18,14 @@ int main() {
   // analysis of this sort below: O(n log n) * cmp: O(n) = O(n^2 log n)
   sort(SA.begin(), SA.end(), [](int a, int b) {  // O(n^2 log n)
     return strcmp(T+a, T+b) < 0;
-  });
+  });                                            // continued below
 
   vi LCP(n);
   LCP[0] = 0;                                    // default value
   for (int i = 1; i < n; ++i) {                  // compute by def, O(n^2)
     int L = 0;                                   // always reset L to 0
-    while (T[SA[i]+L] == T[SA[i-1]+L]) ++L;      // same L-th char, ++L
+    while ((SA[i]+L < n) && (SA[i-1]+L < n) &&
+           (T[SA[i]+L] == T[SA[i-1]+L])) ++L;    // same L-th char, ++L
     LCP[i] = L;
   }
 

diff --git a/ch6/trie.cpp b/ch6/trie.cpp
@@ -8,8 +8,8 @@ struct vertex {
   vertex(char a): alphabet(a), exist(false) { child.assign(26, NULL); }
 };
 
-class Trie {
-private:
+class Trie {                                     // this is TRIE
+private:                                         // NOT Suffix Trie
   vertex* root;
 public:
   Trie() { root = new vertex('!'); }
@@ -59,5 +59,6 @@ int main() {
   printf("'DOG' exist? %d\n", T.search("DOG"));  // 0 (false)
   printf("Starts with 'CA' exist? %d\n", T.startsWith("CA")); // 1 (true)
   printf("Starts with 'Z' exist? %d\n", T.startsWith("Z")); // 0 (false)
+  printf("Starts with 'AT' exist? %d\n", T.startsWith("AT")); // 0 (false) for this Trie, but in a Suffix Trie, we have a suffix "AT" (from "CAT" or "RAT") that starts with "AT"
   return 0;
 }
diff --git a/ch7/points_lines.cpp b/ch7/points_lines.cpp
@@ -199,11 +199,24 @@ bool collinear(point p, point q, point r) {
 }
 
 int main() {
+  vector<point> P;
+  P.emplace_back(2e-9, 0);                       // largest
+  P.push_back({0, 2});                           // smallest
+  P.push_back({1e-9, 1});                        // second smallest
+  sort(P.begin(), P.end());
+  for (auto &pt : P)                             // the result is
+    printf("%.9lf, %.9lf\n", pt.x, pt.y);        // unexpected
+  // change
+  // const double EPS = 1e-9;
+  // to
+  // const double EPS = 1e-10;
+  // to fix that issue, Rule of Thumb: check the required precision
+
   point P1, P2, P3(0, 1); // note that both P1 and P2 are (0.00, 0.00)
-  printf("%d\n", P1 == P2);                                    // true
-  printf("%d\n", P1 == P3);                                   // false
+  printf("%d\n", P1 == P2);                      // true
+  printf("%d\n", P1 == P3);                      // false
 
-  vector<point> P;
+  P.clear();
   P.push_back(point(2, 2));
   P.push_back(point(4, 3));
   P.push_back(point(2, 4));