1+ import java .util .*;
2+ abstract class InfixEvaluation
3+ {
4+ /**
5+ * INFIX EVALUTION
6+ * it will only work when expression has spaces in it
7+ * it will throw exception when no bracket is balanced
8+ *
9+ * test cases
10+ * 2 + 3 => 5
11+ * ( 3 + 3 ) * 2 => 12
12+ **/
13+ public static void main (String [] args )
14+ {
15+ Scanner in = new Scanner (System .in );
16+ System .out .println ("Enter the expression with spaces" );
17+ String expr = in .nextLine (); //input string expression
18+ in .close ();
19+ String [] arr = expr .split (" " ); //parsing the string expression
20+
21+ Stack <Integer > valstack = new Stack <Integer >(); //create the value/operand stack
22+ Stack <Character > opstack = new Stack <Character >(); //create the operator stack
23+
24+ for (int i =0 ;i <arr .length ;i ++) //traversing the exp
25+ {
26+ if (isopr (arr [i ])) //if the arr[i] string is operator
27+ {
28+ if (arr [i ].equals ("(" )) //if left paranthesis found
29+ {
30+ char ch = arr [i ].charAt (0 );
31+ opstack .push (ch ); //push left paranthesis to operator stack
32+ }
33+ else if (arr [i ].equals (")" )) //if right paranthesis found
34+ {
35+ while (opstack .peek ()!='(' )
36+ {
37+ char ch = opstack .pop (); //pop one operator
38+ int a = valstack .pop (); //pop first operand
39+ int b = valstack .pop (); //pop second operand
40+ int result =solve (a ,b ,ch ); //solve the small expression
41+ valstack .push (result ); //push result to value stack
42+ }
43+ opstack .pop ();
44+ }
45+ else //other operator * - + / ^
46+ {
47+ while (!opstack .empty () && precedence (opstack .peek ().toString ())>=precedence (arr [i ]))
48+ {
49+ char ch = opstack .pop (); //pop one operator
50+ int a = valstack .pop (); //pop first operand
51+ int b = valstack .pop (); //pop second operand
52+ int result =solve (a ,b ,ch ); //solve the small expression
53+
54+ valstack .push (result ); //push result to value stack
55+ }
56+ opstack .push (arr [i ].charAt (0 )); //push this operator to operator stack
57+ }
58+ }
59+ else //if number found
60+ {
61+ valstack .push (Integer .parseInt (arr [i ])); //push to value stack
62+ }
63+ }
64+
65+ while (!opstack .empty ())
66+ {
67+ char ch = opstack .pop (); //pop one operator
68+ int a = valstack .pop (); //pop first operand
69+ int b = valstack .pop (); //pop second operand
70+ int result =solve (a ,b ,ch ); //solve the small expression
71+ valstack .push (result ); //push result to value stack
72+ }
73+ System .out .println (valstack .peek ()); //final value present in the value stack
74+ }
75+
76+ /**
77+ * it will solve the expression
78+ *
79+ * @param a for first operand
80+ * @param b for second operand
81+ * @param ch for operator
82+ *
83+ * @return int the result of the epxression
84+ **/
85+ public static int solve (int a ,int b ,char ch )
86+ {
87+ switch (ch )
88+ {
89+ case '+' :
90+ return a +b ;
91+ case '-' :
92+ return a -b ;
93+ case '*' :
94+ return a *b ;
95+ case '/' :
96+ return a /b ;
97+ case '^' :
98+ return (int )Math .pow (a , b );
99+ default :
100+ return -1 ;
101+ }
102+ }
103+
104+ /**
105+ * it will tell the precedence of operators
106+ *
107+ * @param str for operator in string format
108+ *
109+ * @return the precedence value
110+ **/
111+ public static int precedence (String str )
112+ {
113+ switch (str )
114+ {
115+ case "+" :
116+ case "-" :
117+ return 1 ;
118+ case "*" :
119+ case "/" :
120+ return 2 ;
121+ case "^" :
122+ return 3 ;
123+ default :
124+ return -1 ;
125+ }
126+ }
127+
128+ /**
129+ * it will tell wheter the string is operator or not
130+ *
131+ * @param str for operator in string format
132+ *
133+ * @return boolean
134+ **/
135+ public static boolean isopr (String str )
136+ {
137+ switch (str )
138+ {
139+ case "+" :
140+ case "-" :
141+ case "*" :
142+ case "/" :
143+ case "(" :
144+ case ")" :
145+ case "^" :
146+ return true ;
147+ default :
148+ return false ;
149+ }
150+ }
151+ }
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