Merge pull request #55 from SeasClouds/master

[PHP]基本的四则运算 +-*/()

php/Stack/Compute.php

@@ -0,0 +1,78 @@
+<?php
+
+
+
+// 四则运算 +-*/()
+function expression($str)
+{
+    $str = str_replace(' ','',$str);
+    $arr = preg_split('/([\+\-\*\/\(\)])/', $str, -1, PREG_SPLIT_DELIM_CAPTURE | PREG_SPLIT_NO_EMPTY);
+
+    $numStack = [];  // 存放数字
+    $operStack = []; // 存放运算符
+    $operStack[] = NULL;
+
+    for ($i = 0; $i < count($arr); $i++){
+        if (ord($arr[$i]) >= 48 && ord($arr[$i] <= 57)){
+            array_push($numStack, $arr[$i]);
+            continue;
+        }
+        switch ($arr[$i]){
+            case '+':
+            case '-':
+                $arrLen = count($operStack);
+                while ($operStack[$arrLen-1] === '*' || $operStack[$arrLen-1] === '/' || $operStack[$arrLen-1] === '-'){
+                    compute($numStack, $operStack);
+                    $arrLen--;
+                }
+                array_push($operStack, $arr[$i]);
+                break;
+            case '*':
+            case '/':
+            case '(':
+                array_push($operStack, $arr[$i]);
+                break;
+            case ')':
+                $arrLen = count($operStack);
+                while ($operStack[$arrLen-1] !== '('){
+                    compute($numStack, $operStack);
+                    $arrLen--;
+                }
+                array_pop($operStack);
+                break;
+            default:
+                throw new \Exception("不支持的运算符", 1);
+                break;
+        }
+    }
+    
+    $arrLen = count($operStack);
+    while ($operStack[$arrLen-1] !== NULL){  
+        compute($numStack, $operStack);
+        $arrLen--;
+    }
+    echo array_pop($numStack);
+}
+
+//数字栈长度减一，运算符栈长度减一
+function compute(&$numStack, &$operStack){
+    $num = array_pop($numStack);
+    switch (array_pop($operStack)) {
+        case '*':
+            array_push($numStack, array_pop($numStack) * $num);
+            break;
+        case '/':
+            array_push($numStack, array_pop($numStack) / $num);
+            break;
+        case '+':
+            array_push($numStack, array_pop($numStack) + $num);
+            break;
+        case '-':
+            array_push($numStack, array_pop($numStack) - $num);
+            break;
+        
+    }
+}
+expression('-1+2-(1+2*3)');
+echo PHP_EOL;
+eval('echo -1+2-(1+2*3);');