give string s determine valida string s valid start string t transform t s perform follow operation number timesInsert stre abc position t more formally t tleft abc tright t tleft tright Note tleft tright emptyReturn true s valid string return false example 1input s aabcbcoutput trueexplanation abc aabcbcthus aabcbc validExample 2input s abcabcababccoutput trueexplanation abc abcabc abcabcabc abcabcababccThus abcabcababcc validExample 3input s abccbaoutput falseexplanation it impossible abccba operation Constraints1 slength 2 104s consist letter b c