# 2100. Find Good Days to Rob the Bank
###### tags: `Leetcode` `Medium` `Dynamic Programming`
Link: https://leetcode.com/problems/find-good-days-to-rob-the-bank/description/
## 思路
基本型I
prefix[i]表示以security[i]结尾的最长的decreasing序列
suffix[i]表示以security[i]开始的最长的increasing序列
## Code

class Solution {
    public List<Integer> goodDaysToRobBank(int[] security, int time) {
        int n = security.length;
        int[] prefix = new int[n];
        int[] suffix = new int[n];
        for(int i=0; i<n; i++){
            if(i==0 || security[i-1]<security[i]) prefix[i] = 0;
            else prefix[i] = prefix[i-1]+1;
        }
        for(int i=n-1; i>=0; i--){
            if(i==n-1 || security[i+1]<security[i]) suffix[i] = 0;
            else suffix[i] = suffix[i+1]+1;
        }
        List<Integer> ans = new ArrayList<>();
        for(int i=0; i<n; i++){
            if(prefix[i]>=time && suffix[i]>=time) ans.add(i);
        }
        return ans;
    }
}