[LeetCode] 640. Solve the Equation

pf_miles 發(fā)布于2019-08-16 13:38 / 1025人閱讀

Problem

Solve a given equation and return the value of x in the form of string "x=#value". The equation contains only "+", "-" operation, the variable x and its coefficient.

If there is no solution for the equation, return "No solution".

If there are infinite solutions for the equation, return "Infinite solutions".

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

Example 1:
Input: "x+5-3+x=6+x-2"
Output: "x=2"
Example 2:
Input: "x=x"
Output: "Infinite solutions"
Example 3:
Input: "2x=x"
Output: "x=0"
Example 4:
Input: "2x+3x-6x=x+2"
Output: "x=-1"
Example 5:
Input: "x=x+2"
Output: "No solution"

Note

這破題只有一個(gè)考點(diǎn)：正則表達(dá)式

Solution

class Solution {
    public String solveEquation(String equation) {
        String[] sides = equation.split("=");
        String left = sides[0], right = sides[1];
        int[] ls = getCounts(left);
        int[] rs = getCounts(right);
        int countX = ls[0]-rs[0];
        int countNum = rs[1]-ls[1];
        if (countX == 0) {
            if (countNum == 0) return "Infinite solutions";
            else return "No solution";
        }
        
        int x = countNum/countX;
        StringBuilder sb = new StringBuilder();
        sb.append("x=").append(x);
        return sb.toString();
    }
    private int[] getCounts(String str) {
        int[] res = new int[2];
        String[] parts = str.split("(?=[+-])"); //this is what this problem is
        for (String part: parts) {
            if (part.equals("x") || part.equals("+x")) res[0]++;
            else if (part.equals("-x")) res[0]--;
            else if (part.contains("x")) res[0] += Integer.valueOf(part.substring(0, part.indexOf("x")));
            else res[1] += Integer.valueOf(part);
        }
        return res;
    }
}