Validate and Evaluate a + / - Expression (No Parentheses)

Problem: Validate and Evaluate a + / - Expression (No Parentheses) You are given a string s representing an arithmetic expression. The expression: Contains only digits 0-9 and binary operators + and - Contains no parentheses and no other characters Implement a function/program that: Validates whether the expression is well-formed (rules below) If valid, returns the evaluated result; otherwise returns INVALID Validity Rules The expression must consist of non-negative integers and operators alternating, i.e.: num (op num)* No empty tokens are allowed: Cannot start with +/- Cannot end with +/- Cannot contain consecutive operators (e.g. "1++2", "1+-2") Number format: Numbers are in base-10 No leading zeros unless the number is exactly "0" Valid: "0", "10", "101" Invalid: "00", "01", "0123" Range constraint: Each parsed number must be within [MIN, MAX] (the interviewer provides the range; if unspecified, you may assume 32-bit signed [0, 2147483647]) Output If s is valid: output the computed value (left-to-right is sufficient since only +/-) If s is invalid: output INVALID Examples Input: "12+3-4" Output: 11 Input: "0+0" Output: 0 Input: "01+2" Output: INVALID Input: "1+" Output: INVALID Input: "1--2" Output: INVALID Constraints 1 <= len(s) <= 1e5 Target time O(n); space O(1) or O(n) is acceptable. Example Input 12+3-4 Output 11