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$ curl repovive.com/roadmaps/greedy-algorithms/practice-problems/valid-parenthesis-implementation

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#####   ######  #####    ###    #   #  ###  #   #  ######
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##   #  ######  ##       ###      #    ###    #    ######

$ curl repovive.com/roadmaps/greedy-algorithms/practice-problems/valid-parenthesis-implementation

Repovive

Valid Parenthesis - Implementation - Practice Problems | Greedy Algorithms | Repovive

Repovive.

Greedy Algorithms8 sections · 317 units14h total

Open in Course

Valid Parenthesis - Implementation

The code

Here is the solution:

function checkValidString(s)
 lo := 0
 hi := 0
 for c in s
 if c = '(' then
 lo := lo + 1
 hi := hi + 1
 else if c = ')' then
 lo := lo - 1
 hi := hi - 1
 else
 lo := lo - 1
 hi := hi + 1
 if hi < 0 then
 return false
 lo := max(lo, 0)
 return lo = 0

Time: $O(n)$ . Space: $O(1)$ .

The range $[lo, hi]$ covers all possible open counts. If $0$ is in range at the end, some assignment of '*' makes the string valid.