Create Digit DP.cpp

Digit DP.cpp

@@ -0,0 +1,40 @@
+//For Decimals
+
+int sz = 0;
+int x[20];
+int cache[20][2][5];
+
+int dp(int idx, bool less, int taken)
+{
+	if(taken > 3)
+		return 0;
+	if(idx == sz)
+		return 1;
+	int &ans = cache[idx][less][taken];
+	if(ans != -1)
+		return ans;
+	ans = 0;
+	int lo = 0, hi = 9;
+	if(!less)
+		hi = x[idx];
+	for(int i = lo; i <= hi; i++)
+		ans += dp(idx + 1, less | (i < x[idx]), taken + (i > 0));
+	return ans;
+}
+
+int f(int k)
+{
+	memset(cache, -1, sizeof(cache));
+	sz = 0;
+	while(k > 0)
+	{
+		x[sz++] = k % 10;
+		k /= 10;
+	}
+	reverse(x, x + sz);
+	int ans = dp(0, 0, 0);
+	return ans;
+}
+
+//Problem 1: https://codeforces.com/contest/1036/problem/C
+