[poincare] Implement getVariables on Expression

apps/solver/equation_store.h

@@ -21,7 +21,7 @@ private:
     return emptyModel();
   }
   void setModelAtIndex(Shared::ExpressionModel * f, int i) override;
-  static constexpr int k_maxNumberOfEquations = 6;
+  static constexpr int k_maxNumberOfEquations = Poincare::Expression::k_maxNumberOfVariables; // Enable the same number of equations as the number of unknown variables
   Equation m_equations[k_maxNumberOfEquations];;
 };
 

poincare/include/poincare/expression.h

@@ -215,6 +215,17 @@ public:
    * - (-1) if the expression is not a polynome
    * - the degree of the polynome otherwise */
   virtual int polynomialDegree(char symbolName) const;
+  /* getVariables fills the table variables with the variable present in the
+   * expression and returns the number of entries in filled in variables.
+   * For instance getVariables('x+y+2*w/cos(4)') would result in
+   * variables = ['x', 'y', 'w'] and would return 3. If the final number of
+   * variables would overflow the maxNumberOfVariables, getVariables return -1 */
+  static constexpr int k_maxNumberOfVariables = 6;
+  virtual int getVariables(char * variables) const;
+  /* getPolynomialCoefficients fill the table coefficients with the expressions
+   * of the first 4 polynomial coefficients. coefficients is null-terminated
+   * and has up to 4 entries. */
+  //virtual void getPolynomialCoefficients(char symbolName, Expression ** coefficients) const;
 
   /* Comparison */
   /* isIdenticalTo is the "easy" equality, it returns true if both trees have

poincare/include/poincare/symbol.h

@@ -36,6 +36,7 @@ public:
   Type type() const override;
   Expression * clone() const override;
   int polynomialDegree(char symbolName) const override;
+  int getVariables(char * variables) const override;
   Sign sign() const override;
   bool isMatrixSymbol() const;
   bool isScalarSymbol() const;

poincare/src/expression.cpp

@@ -207,6 +207,18 @@ int Expression::polynomialDegree(char symbolName) const {
   return 0;
 }
 
+int Expression::getVariables(char * variables) const {
+  int numberOfVariables = 0;
+  for (int i = 0; i < numberOfOperands(); i++) {
+    int n = operand(i)->getVariables(variables);
+    if (n < 0) {
+      return -1;
+    }
+    numberOfVariables = n > numberOfVariables ? n : numberOfVariables;
+  }
+  return numberOfVariables;
+}
+
 bool Expression::isOfType(Type * types, int length) const {
   for (int i = 0; i < length; i++) {
     if (type() == types[i]) {

poincare/src/symbol.cpp

@@ -113,6 +113,26 @@ int Symbol::polynomialDegree(char symbol) const {
   return 0;
 }
 
+int Symbol::getVariables(char * variables) const {
+  size_t variablesLength = strlen(variables);
+  if (m_name >= 'a' && m_name <= 'z') {
+    char * currentChar = variables;
+    while (*currentChar != 0) {
+      if (*currentChar == m_name) {
+        return variablesLength;
+      }
+      currentChar++;
+    }
+    if (variablesLength < k_maxNumberOfVariables) {
+      variables[variablesLength] = m_name;
+      variables[variablesLength+1] = 0;
+      return variablesLength+1;
+    }
+    return -1;
+  }
+  return variablesLength;
+}
+
 Expression * Symbol::replaceSymbolWithExpression(char symbol, Expression * expression) {
   if (m_name == symbol) {
     Expression * value = expression->clone();

poincare/test/properties.cpp

@@ -77,3 +77,28 @@ QUIZ_CASE(poincare_characteristic_range) {
   assert_parsed_expression_has_characteristic_range("log(cos(40*x))", 9.0f);
   assert_parsed_expression_has_characteristic_range("cos(cos(x))", 360.0f);
 }
+
+void assert_parsed_expression_has_variables(const char * expression, const char * variables) {
+  Expression * e = parse_expression(expression);
+  char variableBuffer[Expression::k_maxNumberOfVariables+1] = {0};
+  int numberOfVariables = e->getVariables(variableBuffer);
+  if (variables == nullptr) {
+    assert(numberOfVariables == -1);
+  } else {
+    assert(numberOfVariables == strlen(variables));
+    char * currentChar = variableBuffer;
+    while (*variables != 0) {
+      assert(*currentChar++ == *variables++);
+    }
+  }
+  delete e;
+}
+
+QUIZ_CASE(poincare_get_variables) {
+  assert_parsed_expression_has_variables("x+y", "xy");
+  assert_parsed_expression_has_variables("x+y+z+2*t", "xyzt");
+  assert_parsed_expression_has_variables("abcdef", "abcdef");
+  assert_parsed_expression_has_variables("abcdefg", nullptr);
+  assert_parsed_expression_has_variables("abcde", "abcde");
+  assert_parsed_expression_has_variables("x^2+2*y+k!*A+w", "xykw");
+}