Create 2999. Count the Number of Powerful Integers1

2999. Count the Number of Powerful Integers1

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+class Solution {
+long long dp[17][2];
+private:
+    long long getAns(string& s,int n,bool tight,int limit,int m,long long t){
+        if(n == m) {
+            if(!tight) return 1ll;
+            else{
+                string temp=s.substr(s.length()-m);
+                long long ele=stoll(temp);
+                if(ele >= t) return 1ll;
+                return 0ll;
+            }
+        }
+        if(n < m) return 0ll;
+        if(dp[n][tight] != -1) return dp[n][tight];
+        int ub=tight ? s[s.length()-n]-'0' : 9;
+        long long ans=0;
+
+            for(int i=0;i<=min(ub,limit) ;i++){
+                ans+=getAns(s,n-1,tight&(ub==i),limit,m,t);
+            }
+
+        return dp[n][tight]=ans;
+    }
+public:
+    long long numberOfPowerfulInt(long long start, long long finish, int limit, string s) {
+        start--;
+
+        string st=to_string(start);
+
+        string f=to_string(finish);
+        long long t=stoll(s);
+        memset(dp,-1,sizeof(dp));
+        long long left=getAns(st,st.length(),1,limit,s.length(),t);
+        memset(dp,-1,sizeof(dp));
+        long long right=getAns(f,f.length(),1,limit,s.length(),t);
+
+        return (right-left);
+    }
+};