0640. Solve the Equation

https://leetcode.com/problems/solve-the-equation

Description

Solve a given equation and return the value of 'x' in the form of a string "x=#value". The equation contains only '+', '-' operation, the variable 'x' and its coefficient. You should return "No solution" if there is no solution for the equation, or "Infinite solutions" if there are infinite solutions for the equation.

If there is exactly one solution for the equation, we ensure that the value of 'x' is an integer.

Example 1:

**Input:** equation = "x+5-3+x=6+x-2"
**Output:** "x=2"

Example 2:

**Input:** equation = "x=x"
**Output:** "Infinite solutions"

Example 3:

**Input:** equation = "2x=x"
**Output:** "x=0"

Example 4:

**Input:** equation = "2x+3x-6x=x+2"
**Output:** "x=-1"

Example 5:

**Input:** equation = "x=x+2"
**Output:** "No solution"

Constraints:

• 3 <= equation.length <= 1000

• equation has exactly one '='.

• equation consists of integers with an absolute value in the range [0, 100] without any leading zeros, and the variable 'x'.

ac

class Solution {
    public String solveEquation(String equation) {
        String[] strs = equation.split("=");
        int[] l = extract(strs[0]);
        int[] r = extract(strs[1]);

        int right = r[0] - l[0];
        int left = l[1] - r[1];

        if (left == 0 && right == 0) {
            return "Infinite solutions";
        } else if (left == 0 && right != 0) {
            return "No solution";
        } else {
            return "x=" + (int)(right / left);
        }
    }

    public int[] extract(String s) {
        String[] strs = s.split("-");
        int val = 0, xval = 0;
        for (int i = 0; i < strs.length; i++) {
            if (strs[i].length() == 0) continue; // skip empty
            String[] vals = strs[i].split("\\+");
            for (int j = 0; j < vals.length; j++) {
                int sign = i != 0 && j == 0 ? -1 : 1;
                if (vals[j].indexOf("x") < 0) { // normal value
                    val += sign * Integer.parseInt(vals[j]);
                } else if ("x".equals(vals[j])) {
                    xval += sign * 1;
                } else {
                    xval += sign * Integer.parseInt(vals[j].replace("x", ""));
                }
            }
        }

        return new int[]{val, xval};
    }
}

/*
1) extract the formula, return {normalVal, x-val}; 2) judge left part and right part
*/