Problem
Validate if a given string can be interpreted as a decimal number.
Some examples:
"0" => true " 0.1 " => true "abc" => false "1 a" => false "2e10" => true " -90e3 " => true " 1e" => false "e3" => false " 6e-1" => true " 99e2.5 " => false "53.5e93" => true " --6 " => false "-+3" => false "95a54e53" => false
Note: It is intended for the problem statement to be ambiguous. You should gather all requirements up front before implementing one. However, here is a list of characters that can be in a valid decimal number:
Numbers 0-9 Exponent - "e" Positive/negative sign - "+"/"-" Decimal point - "."
Of course, the context of these characters also matters in the input.
Solutionclass Solution { public boolean isNumber(String s) { if (s == null || s.length() == 0) return false; s = s.trim(); int len = s.length(); if (len == 0) return false; int signCount = 0; boolean hasE = false; boolean hasNum = false; boolean hasPoint = false; for (int i = 0; i < len; i++) { char ch = s.charAt(i); if (ch >= "0" && ch <= "9") { hasNum = true; } else if (ch == "e" || ch == "E") { if (hasE || !hasNum || i == len-1) return false; hasE = true; } else if (ch == ".") { if (hasPoint || hasE) return false; //0. is true if (i == len-1 && !hasNum) return false; hasPoint = true; } else if (ch == "+" || ch == "-") { //two signs at most; should not appear in the end if (signCount == 2 || i == len-1) return false; //sign appears in the middle but no E/e if (i > 0 && !hasE) return false; signCount++; } else return false; } return true; } }
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