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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.
*/
int countGoodStrings(int low, int high, int zero, int one) {
int mod = 1e9 + 7, ans = 0;
int *dp = (int *)calloc(high + 1, sizeof(int));
dp[0] = 1;
for (int i = 1; i <= high; i++) {
if (i >= one)
dp[i] = (dp[i] + dp[i - one]) % mod;
if (i >= zero)
dp[i] = (dp[i] + dp[i - zero]) % mod;
if (i >= low)
ans = (ans + dp[i]) % mod;
}
free(dp);
return ans;
}
int main() {
printf("%d\n", countGoodStrings(3, 3, 1, 1)); // expect: 8
printf("%d\n", countGoodStrings(2, 3, 1, 2)); // expect: 5
}
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