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Equation.java
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Equation.java
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import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
public class Equation {
private String origEq;
private String idealEq = "";
private List<Term> list = new ArrayList<>();
private float constant = 0;
public Equation(String eq) {
origEq = eq;
IdealizeEq();
sortByKey();
}
public String GetOriginalEquation() {
return origEq;
}
public String GetIdealizedEquation() {
if (idealEq == "") {
StringBuilder sb = new StringBuilder();
for (int k = 0; k < list.size(); k++) {
String varName = list.get(k).getVar();
float coeff = list.get(k).getCoff();
if (k != 0 && coeff >= 0) {
sb.append('+');
}
sb.append(coeff);
sb.append(varName);
}
sb.append("=" + (-1 * constant));
idealEq = sb.toString();
}
return idealEq;
}
public float getConstant() {
return constant;
}
public List<Term> getList() {
return list;
}
public Term getTermByName(String var) {
for (int i = 0; i < list.size(); i++) {
Term t = list.get(i);
if (var.equals(t.getVar())) {
return t;
}
}
return null;
}
private void IdealizeEq() {
String s = origEq.replaceAll(" ", "");
int leftPos = 0;
int sideMultiplier = 1;
for (int i = 0; i < s.length(); i++) {
char c = s.charAt(i);
if (c == '=') {
if (sideMultiplier != 1) {
// syntax error
throw new IllegalArgumentException("2 or more '=' signs");
}
processTerm(s.substring(leftPos, i), sideMultiplier);
sideMultiplier = -1;
leftPos = i + 1;
continue;
}
if (c == '+' || c == '-') {
if (c == '-' && (i == 0 || s.charAt(i - 1) == '=')) {
continue;
}
processTerm(s.substring(leftPos, i), sideMultiplier);
leftPos = i;
}
}
processTerm(s.substring(leftPos), sideMultiplier);
}
private void processTerm(String s, float multiplier) {
String varName = extractVarNameFromString(s);
float coefficient = extractCoeffFromString(s) * multiplier;
if (varName == "") {
constant += coefficient;
} else {
Term t = getTermByName(varName);
if (t != null) {
t.setCoff(t.getCoff() + coefficient);
} else {
t = new Term();
t.setVar(varName);
t.setCoff(coefficient);
list.add(t);
}
}
}
private static float extractCoeffFromString(String s) {
String f = s.replace(extractVarNameFromString(s), "");
if (f.equals("")) {
return 1;
}
if (f.equals("-")) {
return -1;
} else if (f.equals("+")) {
return 1;
}
return Float.parseFloat(f);
}
private static String extractVarNameFromString(String s) {
for (int i = 0; i < s.length(); i++) {
char c = s.charAt(i);
if (!(Character.isDigit(c) || c == '.' || c == '+' || c == '-')) {
return s.substring(i, s.length());
}
}
return ""; // for constants
}
private void sortByKey() {
Collections.sort(list, NameComparator);
}
private static Comparator<Term> NameComparator = new Comparator<Term>() {
@Override
public int compare(Term e1, Term e2) {
return e1.getVar().compareTo(e2.getVar());
}
};
}