src/main/java/com/fishercoder/solutions/_640.java

package com.fishercoder.solutions;

public class _640 {
    public static class Solution1 {
        /**
         * Reference: https://discuss.leetcode.com/topic/95203/concise-java-solution/7
         */
        public String solveEquation(String equation) {
            String[] parts = equation.split("=");
            int[] left = evaluate(parts[0]);
            int[] right = evaluate(parts[1]);
            if (left[0] == right[0] && left[1] == right[1]) {
                return "Infinite solutions";
            } else if (left[0] == right[0]) {
                return "No solution";
            }
            return "x=" + (right[1] - left[1]) / (left[0] - right[0]);
        }

        private int[] evaluate(String part) {
            int[] result = new int[2];//result[0] is the coefficient for x, result[1] is the coefficient for constants
            String[] tokens = part.split("(?=[+-])");  // ()for match group; ?= for match and include in res; [+-] means + or -;
            for (String token : tokens) {
                if (token.equals("+x") || token.equals("x")) {
                    result[0]++;
                } else if (token.equals("-x")) {
                    result[0]--;
                } else if (token.contains("x")) {
                    result[0] += Integer.parseInt(token.substring(0, token.length() - 1));
                } else {
                    result[1] += Integer.parseInt(token);
                }
            }
            return result;
        }
    }
}