In this Leetcode Remove Invalid Parentheses problem solution Given a string s that contains parentheses and letters, remove the minimum number of invalid parentheses to make the input string valid. Return all the possible results. You may return the answer in any order.


Problem solution in Python.

class Solution:
    def removeInvalidParentheses(self, s: str) -> List[str]:
        def check(s):
            count = 0 
            for i in s:
                if i =='(':
                    count += 1
                elif i == ')':
                    count -= 1 
                    if count < 0 :
                        return False
            return count == 0 
        
        dict1 ={s}
        while True:
            temp = []
            for i in dict1:
                if check(i):
                    temp.append(i)
            if temp:
                return temp 
            
            new_set = set()
            for i in dict1:
                for j in range(len(i)):
                    new_set.add(i[:j]+i[j+1:])
            dict1 = new_set



Problem solution in Java.

class Solution {
    private Set<String> candidates;
    private int min;
    private String s;
    
    private boolean isBraket(char c) {
        return c == '(' || c == ')';
    }
    
    public void recurse(StringBuilder buf, int idx, int left, int right, int removed) {
        if (right > left || removed > min) {
            return;
        }
        
        if (idx == s.length()) {
            if (left != right) {
                return;
            }
            
            if (removed < min) {
                candidates.clear();
                min = removed;
            }
            
            candidates.add(buf.toString());
            return;
        }
        
        char c = s.charAt(idx);
        if (isBraket(c)) {
            recurse(buf, idx+1, left, right, removed+1);
            buf.append(c);
            boolean isLeft = (c == '(');
            recurse(buf
                    , idx+1
                    , isLeft ? left + 1 : left
                    , isLeft ? right : right + 1
                    , removed);
        } else {
            buf.append(c);
            recurse(buf, idx+1, left, right, removed);
        }
        buf.deleteCharAt(buf.length()-1);
    }
    
    public List<String> removeInvalidParentheses(String s) {
        this.s = s;
        this.min = Integer.MAX_VALUE;
        this.candidates = new HashSet<>();
        
        recurse(new StringBuilder(), 0, 0, 0, 0);
        return new ArrayList<>(this.candidates);
    }
}


Problem solution in C++.

int getmin(string str)
{
	stack<char> st;
	st.push('a');
	for (int i=0;i<str.size();i++)
	{
		char ch = str[i];
		if (ch == '(')
		{
			st.push(ch);
		} else if ( ch == ')')
		{
			if ( st.top() == '(')
			{
				st.pop();
			} else {
				st.push(')');
			}
		}
	}
	return st.size()-1;
}


Problem solution in C.

void traverse(char* s, int len, int start, int left, int right, int pair, char* stack, int top, char*** arr, int *returnSize)
{
    if(start == len)
    {
        if(!left && !right && !pair)
        {
            int size = top+1;
            char *t = (char*)malloc(sizeof(char)*(size+1));
            for(int i = 0; i < size; i++)
                t[i] = stack[i];
            t[size] = '\0';
            int i = 0;
            while(i < *returnSize)
            {
                if(!strcmp(t, (*arr)[i]))
                    break;
                i++;
            }
            if(i == *returnSize)
            {
                *returnSize += 1;
                *arr = (char**)realloc(*arr, sizeof(char*)*(*returnSize));
                (*arr)[*returnSize-1] = t;
            }
        }
        return ;
    }
    char c = s[start];
    if(c == '(')
    {
        if(left)
            traverse(s, len, start+1, left-1, right, pair, stack, top, arr, returnSize);
        stack[top+1] = c;
        traverse(s, len, start+1, left, right, pair+1, stack, top+1, arr, returnSize);
    }
    else if(c == ')')
    {
        if(right) =
            traverse(s, len, start+1, left, right-1, pair, stack, top, arr, returnSize);
        if(pair)
        {
            stack[top+1] = c;
            traverse(s, len, start+1, left, right, pair-1, stack, top+1, arr, returnSize);
        }
    }
    else
    {
        stack[top+1] = c;
        traverse(s, len, start+1, left, right, pair, stack, top+1, arr, returnSize);
    }
}

char** removeInvalidParentheses(char* s, int* returnSize)
{
    char** arr = (char**)malloc(sizeof(char*));
    *returnSize = 0;
    int left=0, right=0;
    for(int i = 0; s[i]; i++) 
    {
        if(s[i] == '(') left++;
        else if(s[i] == ')')
        {
            if(left) left--;
            else right++;
        }
    }
    int len = strlen(s);
    char *stack = (char*)malloc(sizeof(char)*len);
    int top = -1;
    traverse(s, len, 0, left, right, 0, stack, top, &arr, returnSize);
    return arr;
}