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150. Evaluate Reverse Polish Notation #48
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47 changes: 47 additions & 0 deletions
src/0150_evaluate_reverse_polish_notation/evaluate_reverse_polish_notation.go
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,47 @@ | ||
| /* | ||
| 150. Evaluate Reverse Polish Notation | ||
| https://leetcode.com/problems/evaluate-reverse-polish-notation/ | ||
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| Evaluate the value of an arithmetic expression in Reverse Polish Notation. | ||
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| Valid operators are +, -, *, /. Each operand may be an integer or another expression. | ||
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| Note: | ||
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| Division between two integers should truncate toward zero. | ||
| 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. | ||
| */ | ||
| // time: 2019年01月07日 | ||
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| package evaluatereversepolishnotation | ||
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| import "strconv" | ||
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| // stack | ||
| // time complexity: O(n) | ||
| // space complexity: O(n) | ||
| func evalRPN(tokens []string) int { | ||
| stack := make([]int, len(tokens)) | ||
| top := -1 | ||
| for i := 0; i < len(tokens); i++ { | ||
| switch ch := tokens[i]; ch { | ||
| case "+": | ||
| stack[top-1] += stack[top] | ||
| top-- | ||
| case "-": | ||
| stack[top-1] -= stack[top] | ||
| top-- | ||
| case "*": | ||
| stack[top-1] *= stack[top] | ||
| top-- | ||
| case "/": | ||
| stack[top-1] /= stack[top] | ||
| top-- | ||
| default: | ||
| top++ | ||
| stack[top], _ = strconv.Atoi(ch) | ||
| } | ||
| } | ||
| return stack[0] | ||
| } |
20 changes: 20 additions & 0 deletions
src/0150_evaluate_reverse_polish_notation/evaluate_reverse_polish_notation_test.go
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,20 @@ | ||
| package evaluatereversepolishnotation | ||
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| import "testing" | ||
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| func TestEvalRPN(t *testing.T) { | ||
| testCases := [][]string{ | ||
| {"2", "1", "+", "3", "*"}, | ||
| {"4", "13", "5", "/", "+"}, | ||
| {"10", "6", "9", "3", "+", "-11", "*", "/", "*", "17", "+", "5", "+"}, | ||
| {"4", "3", "-"}, | ||
| } | ||
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| expected := []int{9, 6, 22, 1} | ||
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| for index, tokens := range testCases { | ||
| if res := evalRPN(tokens); res != expected[index] { | ||
| t.Errorf("expected %d, got %d", expected[index], res) | ||
| } | ||
| } | ||
| } |
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