46 lines
1.5 KiB
Java
46 lines
1.5 KiB
Java
import java.util.Stack;
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public class ShuntingYard {
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public static void main(String[] args) {
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String infix = "3 + 4 * 2 / ( 1 - 5 ) ^ 2 ^ 3";
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System.out.printf("infix: %s%n", infix);
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System.out.printf("postfix: %s%n", infixToPostfix(infix));
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}
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static String infixToPostfix(String infix) {
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final String ops = "-+/*^";
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StringBuilder sb = new StringBuilder();
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Stack<Integer> s = new Stack<>();
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for (String token : infix.split("\\s")) {
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char c = token.charAt(0);
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int idx = ops.indexOf(c);
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if (idx != -1 && token.length() == 1) {
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if (s.isEmpty())
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s.push(idx);
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else {
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while (!s.isEmpty()) {
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int prec2 = s.peek() / 2;
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int prec1 = idx / 2;
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if (prec2 > prec1 || (prec2 == prec1 && c != '^'))
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sb.append(ops.charAt(s.pop())).append(' ');
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else break;
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}
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s.push(idx);
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}
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} else if (c == '(') {
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s.push(-2);
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} else if (c == ')') {
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while (s.peek() != -2)
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sb.append(ops.charAt(s.pop())).append(' ');
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s.pop();
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} else {
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sb.append(token).append(' ');
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}
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}
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while (!s.isEmpty())
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sb.append(ops.charAt(s.pop())).append(' ');
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return sb.toString();
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}
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}
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