basic-calculator

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Algorithms

Given a string <code>s</code> representing a valid expression, implement a basic calculator to evaluate it, and return the result of the evaluation.

Note: You are not allowed to use any built-in function which evaluates strings as mathematical expressions, such as <code>eval()</code>.

&nbsp;
Example 1:

<pre>
Input: s = &quot;1 + 1&quot;
Output: 2
</pre>

Example 2:

<pre>
Input: s = &quot; 2-1 + 2 &quot;
Output: 3
</pre>

Example 3:

<pre>
Input: s = &quot;(1+(4+5+2)-3)+(6+8)&quot;
Output: 23
</pre>

&nbsp;
Constraints:

<ul>
	<li><code>1 &lt;= s.length &lt;= 3 * 105</code></li>
	<li><code>s</code> consists of digits, <code>&#39;+&#39;</code>, <code>&#39;-&#39;</code>, <code>&#39;(&#39;</code>, <code>&#39;)&#39;</code>, and <code>&#39; &#39;</code>.</li>
	<li><code>s</code> represents a valid expression.</li>
	<li><code>&#39;+&#39;</code> is not used as a unary operation (i.e., <code>&quot;+1&quot;</code> and <code>&quot;+(2 + 3)&quot;</code> is invalid).</li>
	<li><code>&#39;-&#39;</code> could be used as a unary operation (i.e., <code>&quot;-1&quot;</code> and <code>&quot;-(2 + 3)&quot;</code> is valid).</li>
	<li>There will be no two consecutive operators in the input.</li>
	<li>Every number and running calculation will fit in a signed 32-bit integer.</li>
</ul>

calculate

Basic Calculator

Evaluate Reverse Polish Notation

evaluate-reverse-polish-notation

逆波兰表达式求值

Basic Calculator II

basic-calculator-ii

基本计算器 II

Different Ways to Add Parentheses

different-ways-to-add-parentheses

为运算表达式设计优先级

Expression Add Operators

expression-add-operators

给表达式添加运算符

Basic Calculator III

basic-calculator-iii

基本计算器 III

The Score of Students Solving Math Expression

the-score-of-students-solving-math-expression

解出数学表达式的学生分数

Minimize Result by Adding Parentheses to Expression

minimize-result-by-adding-parentheses-to-expression

向表达式添加括号后的最小结果

Stack

Recursion

Math

String

&#32473;&#20320;&#19968;&#20010;&#23383;&#31526;&#20018;&#34920;&#36798;&#24335; <code>s</code> &#65292;&#35831;&#20320;&#23454;&#29616;&#19968;&#20010;&#22522;&#26412;&#35745;&#31639;&#22120;&#26469;&#35745;&#31639;&#24182;&#36820;&#22238;&#23427;&#30340;&#20540;&#12290;

&#27880;&#24847;:&#19981;&#20801;&#35768;&#20351;&#29992;&#20219;&#20309;&#23558;&#23383;&#31526;&#20018;&#20316;&#20026;&#25968;&#23398;&#34920;&#36798;&#24335;&#35745;&#31639;&#30340;&#20869;&#32622;&#20989;&#25968;&#65292;&#27604;&#22914; <code>eval()</code> &#12290;

&nbsp;

&#31034;&#20363; 1&#65306;

<pre>
&#36755;&#20837;&#65306;s = "1 + 1"
&#36755;&#20986;&#65306;2
</pre>

&#31034;&#20363; 2&#65306;

<pre>
&#36755;&#20837;&#65306;s = " 2-1 + 2 "
&#36755;&#20986;&#65306;3
</pre>

&#31034;&#20363; 3&#65306;

<pre>
&#36755;&#20837;&#65306;s = "(1+(4+5+2)-3)+(6+8)"
&#36755;&#20986;&#65306;23
</pre>

&nbsp;

&#25552;&#31034;&#65306;

<ul>
	<li><code>1 &lt;= s.length &lt;= 3&nbsp;* 105</code></li>
	<li><code>s</code> &#30001;&#25968;&#23383;&#12289;<code>'+'</code>&#12289;<code>'-'</code>&#12289;<code>'('</code>&#12289;<code>')'</code>&#12289;&#21644; <code>' '</code> &#32452;&#25104;</li>
	<li><code>s</code> &#34920;&#31034;&#19968;&#20010;&#26377;&#25928;&#30340;&#34920;&#36798;&#24335;</li>
	<li><code>'+'</code>&nbsp;&#19981;&#33021;&#29992;&#20316;&#19968;&#20803;&#36816;&#31639;(&#20363;&#22914;&#65292; <code>"+1"</code>&nbsp;&#21644; <code>"+(2 + 3)"</code>&nbsp;&#26080;&#25928;)</li>
	<li><code>'-'</code>&nbsp;&#21487;&#20197;&#29992;&#20316;&#19968;&#20803;&#36816;&#31639;(&#21363; <code>"-1"</code>&nbsp;&#21644; <code>"-(2 + 3)"</code>&nbsp;&#26159;&#26377;&#25928;&#30340;)</li>
	<li>&#36755;&#20837;&#20013;&#19981;&#23384;&#22312;&#20004;&#20010;&#36830;&#32493;&#30340;&#25805;&#20316;&#31526;</li>
	<li>&#27599;&#20010;&#25968;&#23383;&#21644;&#36816;&#34892;&#30340;&#35745;&#31639;&#23558;&#36866;&#21512;&#20110;&#19968;&#20010;&#26377;&#31526;&#21495;&#30340; 32&#20301; &#25972;&#25968;</li>
</ul>

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PL/B Language Development and Support