Update count-of-integers.cpp

Author: kamyu104

C++/count-of-integers.cpp

@@ -3,6 +3,45 @@
 
 // combinatorics, dp
 class Solution {
+public:
+    int count(string num1, string num2, int min_sum, int max_sum) {
+        static const int MOD = 1e9 + 7;
+        const auto& check = [&](const auto& x) {
+            const auto& total = accumulate(cbegin(x), cend(x), 0, [](const auto& accu, const auto& c) {
+                return accu + (c - '0');
+            });
+            return min_sum <= total && total <= max_sum;
+        };
+
+        const auto& f = [&](const auto& x) {
+            vector<vector<int>> dp(2, vector<int>(max_sum + 1));
+            dp[0][0] = dp[1][0] = 1;
+            for (int i = size(x) - 1; i >= 0; --i) {
+                vector<vector<int>> new_dp(2, vector<int>(max_sum + 1));
+                for (int t = 0; t < 2; ++t) {
+                    for (int total = 0; total <= max_sum; ++total) {
+                        for (int d = 0; d <= min((t == 1 ? x[i] - '0' : 9), total); ++d) {
+                            new_dp[t][total] = (new_dp[t][total] + dp[static_cast<int>(t && d == x[i] - '0')][total - d]) % MOD;
+                        }
+                    }
+                }
+                dp = move(new_dp);
+            }
+            int result = 0;
+            for (int total = min_sum; total <= max_sum; ++total) {
+                result = (result + dp[1][total]) % MOD;
+            }
+            return result;
+        };
+
+        return (((f(num2) - f(num1)) % MOD + MOD) % MOD + check(num1)) % MOD;
+    }
+};
+
+// Time:  O(n * m), m = max_sum
+// Space: O(m)
+// combinatorics, dp
+class Solution2 {
 public:
     int count(string num1, string num2, int min_sum, int max_sum) {
         static const int MOD = 1e9 + 7;