Spoj Transform The Expression Problem

TransforTheExpression.java

package com.algorithms;

/**
* @Author Mehdi Maick
* Created on 18/09/2016.
*/

import java.util.*;
import java.io.*;

public class TransforTheExpression {

    public static int preced(char a) {
        if (a == '+') return 0;
        if (a == '-') return 1;
        if (a == '*') return 2;
        if (a == '/') return 3;
        if (a == '^') return 4;
        return 10;
    }

    public static boolean isOp(char a) {
        return (a == '+' || a == '-' || a == '/' || a == '*' || a == '^');
    }

    public static void solve(FastReader fs, PrintWriter pw) {
        int t = fs.nextInt();
        char[] exp;
        while (t-- > 0) {
            exp = fs.nextLine().trim().toCharArray();
            pw.println(evaluate(exp));
        }
    }

    private static String evaluate(char[] s) {
        StringBuilder sb = new StringBuilder();
        Stack<Character> st = new Stack<>();
        for (int i = 0; i < s.length; i++) {
            if (s[i] == '(') {
                st.add(s[i]);
            } else if (s[i] == ')') {
                while (st.peek() != '(')
                    sb.append(st.pop());
                st.pop();
            } else if (isOp(s[i])) {
                if (st.empty()) {
                    st.push(s[i]);
                } else {
                    if (preced(st.peek()) > preced(s[i])) {
                        while (preced(st.peek()) > preced(s[i]) && st.peek() != '(')
                            sb.append(st.pop());
                        st.add(s[i]);
                    } else {
                        st.push(s[i]);
                    }
                }
            } else {
                sb.append(s[i]);
            }
        }
        while (!st.empty())
            sb.append(st.pop());
        return sb.toString();
    }

    public static void main(String[] args) throws Exception {
        FastReader fs = new FastReader(System.in);
        PrintWriter pw = new PrintWriter(new OutputStreamWriter(System.out));

        solve(fs, pw);

        fs.close();
        pw.close();
    }

    static class FastReader {

        BufferedReader reader;
        StringTokenizer st;

        FastReader(InputStream stream) {
            reader = new BufferedReader(new InputStreamReader(stream));
            st = null;
        }

        String next() {
            while (st == null || !st.hasMoreTokens()) {
                try {
                    String line = reader.readLine();
                    if (line == null) {
                        return null;
                    }
                    st = new StringTokenizer(line);
                } catch (Exception e) {
                    throw new RuntimeException();
                }
            }
            return st.nextToken();
        }

        String nextLine() {
            String s = null;
            try {
                s = reader.readLine();
            } catch (IOException e) {
                e.printStackTrace();
            }
            return s;
        }

        int nextInt() {
            return Integer.parseInt(next());
        }

        long nextLong() {
            return Long.parseLong(next());
        }

        double nextDouble() {
            return Double.parseDouble(next());
        }

        char nextChar() {
            return next().charAt(0);
        }

        int[] nextIntArray(int n) {
            int[] arr = new int[n];
            int i = 0;
            while (i < n) {
                arr[i++] = nextInt();
            }
            return arr;
        }

        long[] nextLongArray(int n) {
            long[] arr = new long[n];
            int i = 0;
            while (i < n) {
                arr[i++] = nextLong();
            }
            return arr;
        }

        int[] nextIntArrayOneBased(int n) {
            int[] arr = new int[n + 1];
            int i = 1;
            while (i <= n) {
                arr[i++] = nextInt();
            }
            return arr;
        }

        long[] nextLongArrayOneBased(int n) {
            long[] arr = new long[n + 1];
            int i = 1;
            while (i <= n) {
                arr[i++] = nextLong();
            }
            return arr;
        }

        void close() {
            try {
                reader.close();
            } catch (IOException e) {
                System.err.println("There's been an error trying closing the reader ");
                e.printStackTrace();
            }
        }
    }


}