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# Solve the Equation

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

**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

```
按特定匹配条件split
String[] tokens = s.split("(?=[+-])");
```

See Comments

## Code

```java
class Solution {
    /*
    x +5 -2x = 6 -3x;
    leftPart : tokens= { x, +5, -2x}; coefficient for x = 1-2 =-1; constant = 5;
    rightPart: tokens= {6, -3x}; coefficient for x = -3; constant = 6;
    final result = (6-5)/ (-1 - (-3))
    */
    public String solveEquation(String equation) {
        String[] parts = equation.split("=");
        int[] leftPart = evaluate(parts[0]);
        int[] rightPart = evaluate(parts[1]);
        if (leftPart[0] == rightPart[0] &&
            leftPart[1] == rightPart[1]) {
            return "Infinite solutions";
        } else if (leftPart[0] == rightPart[0]){
            return "No solution";
        }
        return "x="+ (rightPart[1] - leftPart[1]) / (leftPart[0] - rightPart[0]);
    }

    private int[] evaluate(String s) {
        String[] tokens = s.split("(?=[+-])");  
        // ()for match group; ?= for match and include in res; [+-] means + or -;
        int[] res = new int[2];
        for(String token : tokens) {
            if (token.equals("+x") || token.equals("x")) { 
                res[0]++; // x means 1x
            } else if (token.equals("-x")) {
                res[0]--;// -x means -1x
            } else if (token.contains("x")) { // +kx or -kx to get k
                res[0] += Integer.parseInt(token.substring(0, token.length() - 1)); 
            } else {
                res[1] += Integer.parseInt(token);
            }
        }

        return res;
    }
}
```


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