Merge pull request #72 from ashutosh-3474/mediumday11

chore: solved medium day 11 task

Medium/Day11/Solution.cpp

@@ -1 +1,57 @@
-// Write Your code here
+// Write Your code here#include <bits/stdc++.h>
+
+using namespace std;
+typedef long long ll;
+const int maxN = 20;
+
+bool tight[maxN];
+ll dp[10][maxN];
+
+ll solve(ll x){
+    if(x <= 10) return x;
+
+    vector<int> D;
+    memset(dp, 0, sizeof(dp));
+    memset(tight, 0, sizeof(tight));
+    for(int i = 0; x; i++){
+        D.push_back(x%10);
+        x /= 10;
+    }
+    reverse(D.begin(), D.end());
+    int N = (int) D.size();
+
+    tight[0] = true;
+    for(int i = 1; i < N; i++)
+        tight[i] = tight[i-1] && (D[i] != D[i-1]);
+    for(int d = 1; d < D[0]; d++)
+        dp[d][0] = 1;
+
+    for(int i = 1; i < N; i++){
+        // Prefix [0..i-1] is same as X
+        if(tight[i-1])
+            for(int d = 0; d < D[i]; d++)
+                if(d != D[i-1])
+                    dp[d][i]++;
+
+        // Prefix [0..i-1] is all leading zeros
+        for(int d = 1; d <= 9; d++)
+            dp[d][i]++;
+
+        //  All other cases
+        for(int d1 = 0; d1 <= 9; d1++)
+            for(int d2 = 0; d2 <= 9; d2++)
+                if(d1 != d2)
+                    dp[d2][i] += dp[d1][i-1];
+    }
+
+    ll cnt = tight[N-1];
+    for(int d = 0; d <= 9; d++)
+        cnt += dp[d][N-1];
+    return cnt;
+}
+
+int main(){
+    ll a, b;
+    scanf("%lld %lld", &a, &b);
+    printf("%lld\n", solve(b) - solve(a-1));
+}