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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
#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
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