# Check If Word Is Valid After Substitutions in C++

Suppose we are given that the string "abc" is valid. So from any valid string V, we can divide V into two pieces X and Y such that X + Y is same as V. (X or Y may be empty.). Then, X + "abc" + Y is also valid. So for example S = "abc", then examples of valid strings are: "abc", "aabcbc", "abcabc", "abcabcababcc". And some examples of invalid strings are: "abccba", "ab", "cababc", "bac". We have to check true if and only if the given string S is valid.

So if the input is like “abcabcababcc”, then that is valid, so output will be true.

To solve this, we will follow these steps −

• define a stack st

• for i in range 0 to size of S

• if st is empty or S[i] is not same as ‘c’, then push S[i] into stack

• otherwise

• insert c into the st

• while size of st >= 3

• c := top of st and pop the top element from st

• b := top of st and pop the top element from st

• a := top of st and pop the top element from st

• temp := temp concatenate with a

• temp := temp concatenate with b

• temp := temp concatenate with c

• if temp is “abc”, then go for next iteration

• otherwise

• push a, then b, then c into st, and break the loop

• return true, when the st is empty, otherwise return false

Let us see the following implementation to get better understanding −

## Example

Live Demo

#include <bits/stdc++.h>
using namespace std;
class Solution {
public:
bool isValid(string S) {
stack <char> st;
for(int i = 0; i < S.size(); i++){
if(st.empty() || S[i] != 'c'){
st.push(S[i]);
}else{
st.push('c');
while(st.size() >= 3){
char c = st.top();
st.pop();
char b = st.top();
st.pop();
char a = st.top();
st.pop();
string temp = "";
temp += a;
temp += b;
temp += c;
if(temp == "abc"){
continue;
}else{
st.push(a);
st.push(b);
st.push(c);
break;
}
}
}
}
return st.empty();
}
};
main(){
Solution ob;
cout << (ob.isValid("abcabcababcc"));
}

## Input

“abcabcababcc”

## Output

1