1function solveEquation(equation) {
2    const parse = (s) => {
3        let parts = { x_coef: 0, const: 0 };
4        let num = '';
5        let sign = 1;
6        for (let i = 0; i <= s.length; i++) {
7            if (i < s.length && (s[i] === '+' || s[i] === '-')) {
8                if (num) parts.const += sign * parseInt(num, 10);
9                num = '';
10                sign = s[i] === '+' ? 1 : -1;
11            } else if (i < s.length && s[i].match(/[0-9]/)) {
12                num += s[i];
13            } else {
14                if (s[i] === 'x') {
15                    if (num === '') num = '1';
16                    parts.x_coef += sign * parseInt(num, 10);
17                } else if (num) {
18                    parts.const += sign * parseInt(num, 10);
19                }
20                num = '';
21            }
22        }
23        return parts;
24    };
25
26    const [left, right] = equation.split('=');
27    const leftParts = parse(left + '+');
28    const rightParts = parse(right + '+');
29
30    const x_coef = leftParts.x_coef - rightParts.x_coef;
31    const constant = rightParts.const - leftParts.const;
32
33    if (x_coef === 0) {
34        return constant === 0 ? 'Infinite solutions' : 'No solution';
35    } else {
36        return `x=${constant / x_coef}`;
37    }
38}

1public class Solution {
2    public string SolveEquation(string equation) {
3        (int xCoefL, int constL) = ParseEquation(equation.Split('=')[0]);
4        (int xCoefR, int constR) = ParseEquation(equation.Split('=')[1]);
5
        int xCoef = xCoefL - xCoefR;
        int constant = constR - constL;

        if (xCoef == 0) {
            return constant == 0 ? "Infinite solutions" : "No solution";
        } else {
            return "x=" + (constant / xCoef).ToString();
        }
    }

    private (int, int) ParseEquation(string side) {
        int xCoef = 0, constant = 0;
        int sign = 1;
        int i = 0;
        while (i < side.Length) {
            if (side[i] == '+') {
                sign = 1;
                i++;
            } else if (side[i] == '-') {
                sign = -1;
                i++;
            }

            int val = 0;
            bool isX = false;
            if (i < side.Length && char.IsDigit(side[i])) {
                while (i < side.Length && char.IsDigit(side[i])) {
                    val = val * 10 + (side[i] - '0');
                    i++;
                }
            } else {
                val = 1;
            }

            if (i < side.Length && side[i] == 'x') {
                isX = true;
                i++;
            }

            if (isX) {
                xCoef += sign * val;
            } else {
                constant += sign * val;
            }
        }
        return (xCoef, constant);
    }
}