640.js

//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 eq
//uation, 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 o
//f '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] wi
//thout any leading zeros, and the variable 'x'.
//
// Related Topics 数学
// 👍 71 👎 0


//leetcode submit region begin(Prohibit modification and deletion)
/**
 * @param {string} equation
 * @return {string}
 */
var solveEquation = function (equation) {
    const [left, right] = equation.split('=')

    let xp = 0;
    let np = 0;

    function process(s, xop, nop) {
        if (!['+', '-'].includes(s[0])) s = '+' + s;
        while (s.length) {
            let m = s.match(/^([+-])(\d*)?([x]?)/)
            if (m && m.length) {
                let p = Number.parseInt(m[1] + '1');
                let n = m[2] == undefined ? 1 : m[2];

                if (m[3] == 'x') {
                    p = xop * p;
                    xp = xp + n * p;
                } else {
                    p = nop * p;
                    np = np + n * p;
                }
                s = s.slice(m[0].length);
            }
        }
    }

    process(left, 1, -1);
    process(right, -1, 1);

    if (xp == 0 && np == 0) {
        return 'Infinite solutions';
    } else if (xp == 0) {
        return 'No solution';
    } else {
        return 'x=' + np / xp;
    }
};
//leetcode submit region end(Prohibit modification and deletion)
// const r = solveEquation('x+5-3+x=6+x-2')
const r = solveEquation('-x=1');
console.log(`r: ` + JSON.stringify(r, null, 4) + '\n')