class Solution { static long [] dp; static int mod = (int)(1e9+7); static int countGoodStrings(int low, int high, int zero, int one) { dp = new long [(int)(1e6)]; Arrays.fill(dp, -1); return (int)getResult(low, high, zero, one, 0); } static long getResult(int low, int high, int x, int y, int cur){ if(cur > high) return 0; if(dp[cur] != -1) return dp[cur]; long ans = (cur >= low && cur <= high? 1:0) + getResult(low, high, x, y, cur + x) + getResult(low, high, x, y, cur + y); return dp[cur] = ans % mod; } }