# 2466. Count Ways To Build Good Strings
###### tags: `Leetcode` `Medium` `Dynamic Programming`
Link: https://leetcode.com/problems/count-ways-to-build-good-strings/description/
## 思路
和[0518. Coin Change 2](https://hackmd.io/azimrNJRRUK0CBaC2d0Ivg)差不多

## Code

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