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Number of Valid Subarrays in C++
Suppose we have an array A of integers, we have to find the number of non-empty continuous subarrays that satisfy this condition: The leftmost element of the subarray is not larger than other elements in the subarray.
So, if the input is like [1,4,2,5,3], then the output will be 11, as there are 11 valid subarrays, they are like [1],[4],[2],[5],[3],[1,4],[2,5],[1,4,2],[2,5,3],[1,4,2,5],[1,4,2,5,3].
To solve this, we will follow these steps −
ret := 0
n := size of nums
Define one stack st
for initialize i := 0, when i < size of nums, update (increase i by 1), do −
x := nums[i]
while (not st is empty and x < top element of st), do −
delete element from st
insert x into st
ret := size of st + ret
return ret
Let us see the following implementation to get better understanding −
Example
#include <bits/stdc++.h>
using namespace std;
class Solution {
public:
int validSubarrays(vector<int>& nums) {
int ret = 0;
int n = nums.size();
stack <int> st;
for(int i = 0; i < nums.size(); i++){
int x = nums[i];
while(!st.empty() && x < st.top()) st.pop();
st.push(x);
ret += st.size();
}
return ret;
}
};
main(){
Solution ob;
vector<int> v = {1,4,2,5,3};
cout << (ob.validSubarrays(v));
}Input
{1,4,2,5,3}Output
11
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