2327. Number of People Aware of a Secret.cpp

Author: emcc2302

2327. Number of People Aware of a Secret.cpp

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+class Solution {
+public:
+    int peopleAwareOfSecret(int n, int delay, int forget) {
+        const long long MOD = 1000000007LL;
+        if (n == 1) return 1;
+        vector<long long> dp(n+1);
+        dp[1] = 1;
+        long long window = 0;
+        for (int i = 2; i <= n; ++i) {
+            int enter = i - delay;
+            int exit  = i - forget;
+            if (enter >= 1) window = (window + dp[enter]) % MOD;
+            if (exit >= 1) window = (window - dp[exit] + MOD) % MOD;
+            dp[i] = window;
+        }
+        long long ans = 0;
+        int start = max(1, n - forget + 1);
+        for (int i = start; i <= n; ++i) ans = (ans + dp[i]) % MOD;
+        return (int)ans;
+    }
+};