chore: solved hard day 6 task

hard/day_6/solution.cpp

@@ -1 +1,107 @@
-//Write your code here
+#include<bits/stdc++.h>
+using namespace std;
+#define fo(i,a,b) for(int i=a;i<=b;i++) // Macro for looping from a to b
+
+char leftString[1010], rightString[1010]; // Arrays for storing left and right strings
+int stateCount, transitions[20000][10], suffixLinks[20000], prefixSums[17000][2010], length, n, dp[2005][17000], reachable[2005][17000], leftLength, rightLength; // Variables for counting, storing transitions, and dynamic programming
+
+int newState(int x, int y){
+    return !transitions[x][y] ? transitions[x][y] = ++stateCount : transitions[x][y]; // Function to get or create a new state
+}
+
+void insertStrings(){
+    leftLength = strlen(leftString + 1), rightLength = strlen(rightString + 1); // Get the lengths of left and right strings
+    int x = 0, y = 0; // Initialize states for left and right strings
+    if(leftLength == rightLength){ // If lengths are equal
+        fo(i, 1, leftLength){
+            if(x == y){
+                fo(j, leftString[i] - '0' + 1, rightString[i] - '0' - 1)
+                    prefixSums[newState(x, j)][leftLength - i]++; // Increment count for transitions
+                x = newState(x, leftString[i] - '0'); // Transition to next state
+                y = newState(y, rightString[i] - '0'); // Transition to next state
+            }
+            else{
+                fo(j, leftString[i] - '0' + 1, 9)
+                    prefixSums[newState(x, j)][leftLength - i]++; // Increment count for transitions
+                x = newState(x, leftString[i] - '0'); // Transition to next state
+                fo(j, (i == 1), rightString[i] - '0' - 1)
+                    prefixSums[newState(y, j)][rightLength - i]++; // Increment count for transitions
+                y = newState(y, rightString[i] - '0'); // Transition to next state
+            }
+        }
+        prefixSums[x][0]++; // Increment count for final state
+        if(x != y) prefixSums[y][0]++; // Increment count for final state
+    }
+    else{
+        fo(i, 1, leftLength){
+            fo(j, leftString[i] - '0' + 1, 9)
+                prefixSums[newState(x, j)][leftLength - i]++; // Increment count for transitions
+            x = newState(x, leftString[i] - '0'); // Transition to next state
+        }
+        fo(i, 1, rightLength){
+            fo(j, (i == 1), rightString[i] - '0' - 1)
+                prefixSums[newState(y, j)][rightLength - i]++; // Increment count for transitions
+            y = newState(y, rightString[i] - '0'); // Transition to next state
+        }
+        fo(i, leftLength + 1, rightLength - 1)
+            fo(j, 1, 9)
+                prefixSums[newState(0, j)][i - 1]++; // Increment count for transitions
+        prefixSums[x][0]++; // Increment count for final state
+        prefixSums[y][0]++; // Increment count for final state
+    }
+}
+
+queue<int> bfsQueue; // Queue for BFS
+
+void buildAutomaton(){
+    fo(i, 0, 9) if(transitions[0][i])
+        bfsQueue.push(transitions[0][i]); // Push initial states to the queue
+    while(!bfsQueue.empty()){
+        int currentState = bfsQueue.front();
+        bfsQueue.pop();
+        fo(i, 0, rightLength - 1)
+            prefixSums[currentState][i] += prefixSums[suffixLinks[currentState]][i]; // Update counts using suffix link
+        fo(i, 0, 9){
+            if(transitions[currentState][i]){
+                bfsQueue.push(transitions[currentState][i]);
+                suffixLinks[transitions[currentState][i]] = transitions[suffixLinks[currentState]][i]; // Set suffix link
+            }
+            else transitions[currentState][i] = transitions[suffixLinks[currentState]][i]; // Set transition
+        }
+    }
+    fo(i, 0, stateCount)
+        fo(j, 1, n)
+            prefixSums[i][j] += prefixSums[i][j - 1]; // Compute prefix sums
+}
+
+int main(){
+    scanf("%s%s%d", leftString + 1, rightString + 1, &n); // Input left, right strings, and n
+    insertStrings(); // Construct automaton
+    buildAutomaton(); // Build automaton
+    memset(dp, -32, sizeof(dp)); // Initialize DP table
+    dp[0][0] = 0; // Base case
+    fo(i, 0, n - 1)
+        fo(j, 0, stateCount)
+            if(dp[i][j] >= 0)
+                fo(k, 0, 9)
+                    dp[i + 1][transitions[j][k]] = max(dp[i + 1][transitions[j][k]], dp[i][j] + prefixSums[transitions[j][k]][n - i - 1]); // DP transition
+    int result = -1e9; // Initialize result
+    fo(i, 0, stateCount)
+        result = max(result, dp[n][i]); // Update result
+    printf("%d\n", result); // Output result
+
+    fo(i, 0, stateCount)
+        reachable[n][i] = (result == dp[n][i]); // Mark states achieving the result
+    for(int i = n - 1; i; i--)
+        fo(j, 0, stateCount)
+            fo(k, 0, 9)
+                reachable[i][j] |= reachable[i + 1][transitions[j][k]] && (dp[i + 1][transitions[j][k]] == dp[i][j] + prefixSums[transitions[j][k]][n - i - 1]); // Mark states for next iteration
+    int currentState = 0; // Initialize state
+    fo(i, 1, n)
+        fo(k, 0, 9)
+            if(reachable[i][transitions[currentState][k]] && dp[i][transitions[currentState][k]] == dp[i - 1][currentState] + prefixSums[transitions[currentState][k]][n - i]){
+                printf("%d", k); // Output character
+                currentState = transitions[currentState][k]; // Transition to next state
+                break;
+            }
+}