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5 | 5 | import java.util.Stack;
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6 | 6 |
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7 | 7 | /**
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8 |
| - * Evaluate the value of an arithmetic expression in Reverse Polish Notation. |
9 |
| -
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10 |
| - Valid operators are +, -, *, /. Each operand may be an integer or another expression. |
11 |
| -
|
12 |
| - Some examples: |
13 |
| -
|
14 |
| - ["2", "1", "+", "3", "*"] -> ((2 + 1) * 3) -> 9 |
15 |
| - ["4", "13", "5", "/", "+"] -> (4 + (13 / 5)) -> 6 |
16 |
| -
|
| 8 | + * 150. Evaluate Reverse Polish Notation |
| 9 | + * |
| 10 | + * Evaluate the value of an arithmetic expression in Reverse Polish Notation. |
| 11 | + * |
| 12 | + * Valid operators are +, -, *, /. Each operand may be an integer or another expression. |
| 13 | + * |
| 14 | + * Note: |
| 15 | + * |
| 16 | + * Division between two integers should truncate toward zero. |
| 17 | + * The given RPN expression is always valid. That means the expression would always evaluate to a result and there won't be any divide by zero operation. |
| 18 | + * |
| 19 | + * Example 1: |
| 20 | + * |
| 21 | + * Input: ["2", "1", "+", "3", "*"] |
| 22 | + * Output: 9 |
| 23 | + * Explanation: ((2 + 1) * 3) = 9 |
| 24 | + * |
| 25 | + * Example 2: |
| 26 | + * |
| 27 | + * Input: ["4", "13", "5", "/", "+"] |
| 28 | + * Output: 6 |
| 29 | + * Explanation: (4 + (13 / 5)) = 6 |
| 30 | + * |
| 31 | + * Example 3: |
| 32 | + * |
| 33 | + * Input: ["10", "6", "9", "3", "+", "-11", "*", "/", "*", "17", "+", "5", "+"] |
| 34 | + * Output: 22 |
| 35 | + * Explanation: |
| 36 | + * ((10 * (6 / ((9 + 3) * -11))) + 17) + 5 |
| 37 | + * = ((10 * (6 / (12 * -11))) + 17) + 5 |
| 38 | + * = ((10 * (6 / -132)) + 17) + 5 |
| 39 | + * = ((10 * 0) + 17) + 5 |
| 40 | + * = (0 + 17) + 5 |
| 41 | + * = 17 + 5 |
| 42 | + * = 22 |
17 | 43 | */
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18 | 44 | public class _150 {
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19 | 45 |
|
20 |
| - public int evalRPN(String[] tokens) { |
21 |
| - Stack<String> stack = new Stack<String>(); |
22 |
| - Set<String> op = new HashSet(); |
23 |
| - op.add("+"); |
24 |
| - op.add("-"); |
25 |
| - op.add("*"); |
26 |
| - op.add("/"); |
| 46 | + public static class Solution1 { |
| 47 | + public int evalRPN(String[] tokens) { |
| 48 | + Stack<String> stack = new Stack<>(); |
| 49 | + Set<String> op = new HashSet(); |
| 50 | + op.add("+"); |
| 51 | + op.add("-"); |
| 52 | + op.add("*"); |
| 53 | + op.add("/"); |
27 | 54 |
|
28 |
| - int exp = 0; |
29 |
| - String operand1 = ""; |
30 |
| - String operand2 = ""; |
31 |
| - for (int i = 0; i < tokens.length;) { |
32 |
| - while ((i < tokens.length) && (!op.contains(tokens[i]))) { |
33 |
| - stack.push(tokens[i]); |
34 |
| - i++; |
35 |
| - } |
36 |
| - if (i == tokens.length) { |
37 |
| - if (!stack.isEmpty()) { |
38 |
| - return Integer.parseInt(stack.pop()); |
39 |
| - } |
40 |
| - } else if (op.contains(tokens[i])) { |
41 |
| - if (!stack.isEmpty()) { |
42 |
| - operand2 = stack.pop(); |
| 55 | + int exp = 0; |
| 56 | + String operand1 = ""; |
| 57 | + String operand2 = ""; |
| 58 | + for (int i = 0; i < tokens.length; ) { |
| 59 | + while ((i < tokens.length) && (!op.contains(tokens[i]))) { |
| 60 | + stack.push(tokens[i]); |
| 61 | + i++; |
43 | 62 | }
|
44 |
| - if (!stack.isEmpty() && !op.contains(stack.peek())) { |
45 |
| - operand1 = stack.pop(); |
| 63 | + if (i == tokens.length) { |
| 64 | + if (!stack.isEmpty()) { |
| 65 | + return Integer.parseInt(stack.pop()); |
| 66 | + } |
| 67 | + } else if (op.contains(tokens[i])) { |
| 68 | + if (!stack.isEmpty()) { |
| 69 | + operand2 = stack.pop(); |
| 70 | + } |
| 71 | + if (!stack.isEmpty() && !op.contains(stack.peek())) { |
| 72 | + operand1 = stack.pop(); |
| 73 | + } |
| 74 | + if (tokens[i].equals("+")) { |
| 75 | + exp = Integer.parseInt(operand1) + Integer.parseInt(operand2); |
| 76 | + } else if (tokens[i].equals("-")) { |
| 77 | + exp = Integer.parseInt(operand1) - Integer.parseInt(operand2); |
| 78 | + } else if (tokens[i].equals("*")) { |
| 79 | + exp = Integer.parseInt(operand1) * Integer.parseInt(operand2); |
| 80 | + } else if (tokens[i].equals("/")) { |
| 81 | + exp = Integer.parseInt(operand1) / Integer.parseInt(operand2); |
| 82 | + } else { |
| 83 | + exp = Integer.parseInt(operand2); |
| 84 | + } |
| 85 | + stack.push(String.valueOf(exp)); |
| 86 | + i++; |
46 | 87 | }
|
47 |
| - if (tokens[i].equals("+")) { |
48 |
| - exp = Integer.parseInt(operand1) + Integer.parseInt(operand2); |
49 |
| - } else if (tokens[i].equals("-")) { |
50 |
| - exp = Integer.parseInt(operand1) - Integer.parseInt(operand2); |
51 |
| - } else if (tokens[i].equals("*")) { |
52 |
| - exp = Integer.parseInt(operand1) * Integer.parseInt(operand2); |
53 |
| - } else if (tokens[i].equals("/")) { |
54 |
| - exp = Integer.parseInt(operand1) / Integer.parseInt(operand2); |
55 |
| - } else { |
56 |
| - exp = Integer.parseInt(operand2); |
57 |
| - } |
58 |
| - stack.push(String.valueOf(exp)); |
59 |
| - i++; |
60 | 88 | }
|
| 89 | + return Integer.parseInt(stack.pop()); |
61 | 90 | }
|
62 |
| - return Integer.parseInt(stack.pop()); |
63 | 91 | }
|
64 |
| - |
65 | 92 | }
|
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