LeetCode 2954: Count the Number of Infection Sequences Solution
Master LeetCode problem 2954 (Count the Number of Infection Sequences), a hard challenge, with our optimized solutions in Java, C++, and Python. Explore detailed explanations, test your code in our interactive editor, and prepare for coding interviews.
2954. Count the Number of Infection Sequences
Problem Explanation
Explanation:
To solve this problem, we can use dynamic programming. We will iterate over each infected person and calculate the number of ways uninfected people between them can be infected. We will keep track of the number of ways each uninfected person can be infected at each step. At the end, we will sum up the total number of valid infection sequences.
- Initialize a dp array to store the number of ways each uninfected person can be infected at each step.
- Iterate over the infected people positions and calculate the number of ways uninfected people between them can be infected.
- Update the dp array based on the number of ways each uninfected person can be infected.
- Sum up the total number of valid infection sequences.
Time Complexity: O(n)
Space Complexity: O(n)
:
Solution Code
class Solution {
public int countSequences(int n, int[] sick) {
int MOD = 1000000007;
int[] dp = new int[n];
for (int i = 0; i < n; i++) {
dp[i] = 1;
}
for (int s : sick) {
int[] temp = new int[n];
int sum = 0;
for (int i = s - 1; i >= 0; i--) {
sum = (sum + dp[i]) % MOD;
temp[i] = sum;
}
sum = 0;
for (int i = s + 1; i < n; i++) {
sum = (sum + dp[i]) % MOD;
temp[i] = sum;
}
dp = temp;
}
int total = 0;
for (int i = 0; i < n; i++) {
total = (total + dp[i]) % MOD;
}
return total;
}
}Try It Yourself
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