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// 2466. Count Ways To Build Good Strings
#include "leetcode.h"

/*
 * given the integers 'zero, one, low, and high', we can construct a string by
 * starting with an empty string, and then at each step perform either of the
 * following opperations:
 * - append the character 0 'zero' times
 * - append the character 1 'one' times
 * this can be performed any number of times. a good string is a string
 * constructed by the above process having a length between 'low' and 'high'
 * (inclusive). return the number of different good strings that can be
 * constructed. return modulo 10^9+7.
 */

class Solution {
public:
  int countGoodStrings(int low, int high, int zero, int one) {
    vector<int> dp(high + 1, 0);
    dp[0] = 1;
    int mod = 1000000007;
    for (int i = 1; i <= high; ++i) {
      if (i >= zero)
        dp[i] += dp[i - zero] % mod;
      if (i >= one)
        dp[i] += dp[i - one] % mod;
    }
    long long cnt = 0;
    for (int i = low; i <= high; ++i)
      cnt = (cnt + dp[i]) % mod;
    return cnt;
  }
};

int main() {
  Solution obj;
  printf("%d\n", obj.countGoodStrings(3, 3, 1, 1)); // expect: 8
  printf("%d\n", obj.countGoodStrings(2, 3, 1, 2)); // expect: 5
}