Math-640-Solve the Equation

Description:

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"

Best Solution:

class Solution {
public String solveEquation(String equation) {
if(equation == null || equation.length() == 0) return "No solution";
String[] sides = equation.split("=");
int[] left = parse(sides[0]), right = parse(sides[1]);
if(left[0] == right[0]) {
if(left[1] == right[1]) return "Infinite solutions";
return "No solution";
}
int val = (right[1]-left[1])/(left[0]-right[0]);
return "x="+val;
}

private int[] parse(String s) {
int sign = 1, val = 0;
int[] res = new int[2];
for(int i=0; i<s.length(); i++) {
char c = s.charAt(i);
if(c=='x') {
if(i == 0) res[0]++;
else if(s.charAt(i-1) == '-' || s.charAt(i-1) == '+') res[0] += sign;
else res[0] += sign * val;
val = 0;
} else if(c == '-' || c == '+') {
res[1] += sign * val;
val = 0;
sign = c == '-' ? -1 : 1;
} else {
val = val * 10 + c - '0';
}
}
res[1] += sign * val;
return res;
}
}