本文先給出思路與方法，最后將給出完整代碼：
算法綜述：
一、中綴表達(dá)式轉(zhuǎn)后綴表達(dá)式：
1.中綴表達(dá)式要轉(zhuǎn)后綴表達(dá)式，首先需要兩個(gè)stack（棧），其中一個(gè)應(yīng)用于存放字符，另一個(gè)用于存放數(shù)字。
2.讀到數(shù)字直接存入數(shù)字棧中，讀到字符時(shí)，要咸魚(yú)棧內(nèi)前一元素（字符）進(jìn)行比較，當(dāng)當(dāng)前（要存入的字符）優(yōu)先級(jí)大于遷移字符時(shí)才存入，否則（>=）要仿佛將棧內(nèi)元素彈出，并依次存入數(shù)字棧中。
提示：‘（' 的優(yōu)先級(jí)默認(rèn)比所有字符都小。所有字符都可以存在它后面；同時(shí)夜筆所有字符都大，可以存在所有字符后面
3.遇到 ‘）'時(shí)將棧內(nèi)所有字符依次彈出，并存入數(shù)字棧中，知道遇到 ‘（' 為止
4.當(dāng)所有字符、數(shù)字訪問(wèn)完畢時(shí)，棧內(nèi)很可能還會(huì)有剩余的字符，這是將他們一次彈出，并純?nèi)鐢?shù)字棧中
小技巧：
1.存放‘+'，‘-'時(shí)，如果只有當(dāng)前一個(gè)數(shù)位空或者‘（' 時(shí)才進(jìn)行存入操作，否則均彈出。
2.存放 ‘*'，‘/' 時(shí)，只有當(dāng)前一個(gè)數(shù)位 ‘*'，‘/' 時(shí)才彈出其他情況下，均存入。
附上代碼：
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/** 中綴轉(zhuǎn)后綴*/public void topostfix() {// todo auto-generated method stubint sum = 0 ;//用于記入”（）“總個(gè)數(shù)int j = 0 ;//用于讀到”）“時(shí)循環(huán)出棧string outstack = null;charnum.push(null);for( int i = 0 ; i < calculatelength ; i ++){if ( calculate[i].equals("(")) {charnum.push(calculate[i]);sum ++ ;}else if ( calculate[i].equals(")") ) {outstack = charnum.pop();//進(jìn)入前先出一個(gè)while ( !outstack.equals("(") ){num.push(outstack);outstack = charnum.pop();}//最后一次outstack正好接到”（“不入棧sum ++ ;}else if (calculate[i].equals("*")) {outstack = charnum.pop();charnum.push(outstack);while( ( outstack == "*" || outstack == "/" ) && !(outstack == null) ){num.push(outstack);charnum.pop();//由于前第三行又將outstack存入棧中，座椅此處再次彈出outstack = charnum.pop();charnum.push(outstack);}charnum.push("*");}else if (calculate[i].equals("/")) {outstack = charnum.pop();charnum.push(outstack);while( ( outstack == "*" || outstack == "/" ) && !(outstack == null) ){num.push(outstack);charnum.pop();//由于前第三行又將outstack存入棧中，座椅此處再次彈出outstack = charnum.pop();charnum.push(outstack);}charnum.push("/");}else if (calculate[i].equals("+")) {outstack = charnum.pop();charnum.push(outstack);while( !(outstack=="(") && !(outstack == null) ){num.push(outstack);charnum.pop();outstack = charnum.pop();charnum.push(outstack);}charnum.push("+");}else if (calculate[i].equals("-")) {outstack = charnum.pop();charnum.push(outstack);while( !(outstack=="(") && !(outstack == null) ){num.push(outstack);charnum.pop();outstack = charnum.pop();charnum.push(outstack);}charnum.push("-");}else {num.push(calculate[i]);}}outstack = charnum.pop();while ( outstack != null ) {num.push(outstack);outstack = charnum.pop();}calculatelength = calculatelength - sum ;stack<string> zanshi = new stack<>();for(int i = 0 ; i < calculatelength ; i ++ ){zanshi.push(num.pop());}calculatetozero();for(int i = 0 ; i < calculatelength ;i ++ ){calculate[i] = zanshi.pop();}} |
二、后綴表達(dá)式計(jì)算
后綴表達(dá)式計(jì)算只遵循一個(gè)原則：
首先將表達(dá)式存在棧中
遇到符號(hào)時(shí)彈出兩個(gè)相應(yīng)的數(shù)字，進(jìn)行計(jì)算后再次 存入棧內(nèi)
最后棧內(nèi)身下的唯一一個(gè)數(shù)，就是所要求的結(jié)果
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/* * 后綴表達(dá)式求值 */ public string postfix() { int a = 0 , b = 0;//棧中彈出的兩數(shù) int sum ;//求兩數(shù)運(yùn)算 for (int i = 0; i < calculatelength ; i++ ) { if (i == 0) { num.push(calculate[i]); }else if (calculate[i].equals("+") ) { b = integer.parseint(num.pop()); a = integer.parseint(num.pop()); sum = a + b ; num.push(string.valueof(sum)); }else if (calculate[i].equals("-") ) { b = integer.parseint(num.pop()); a = integer.parseint(num.pop()); sum = a - b ; num.push(string.valueof(sum)); }else if (calculate[i].equals("*") ) { b = integer.parseint(num.pop()); a = integer.parseint(num.pop()); sum = a * b ; num.push(string.valueof(sum)); }else if (calculate[i].equals("/") ) { b = integer.parseint(num.pop()); a = integer.parseint(num.pop()); sum = a / b ; num.push(string.valueof(sum)); }else if (calculate[i].equals("%") ) { b = integer.parseint(num.pop()); a = integer.parseint(num.pop()); sum = a / b ; num.push(string.valueof(sum)); }else { num.push(calculate[i]); } } return num.pop(); }} |
最后附上完整代碼
//注：代碼中有很多輸出 方便讀者實(shí)時(shí)查看運(yùn)算過(guò)程中 各內(nèi)容
// 這些輸出導(dǎo)致篇幅較長(zhǎng) 大家看明白后 刪去即可
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public class text { stack<string> num = new stack<>(); //后綴用棧 中轉(zhuǎn)后數(shù)字棧 stack<string> charnum = new stack<>();//中轉(zhuǎn)后字符棧 string []calculate = new string[1000];//存字符串?dāng)?shù)組 int calculatelength = 0 ;//字符串?dāng)?shù)組長(zhǎng)度 public text() { // todo auto-generated constructor stub } //轉(zhuǎn)字符串?dāng)?shù)組 public void tostringarray(string input) { char chararray[] = input.tochararray(); int number = 0;//用于導(dǎo)入多位數(shù) int j = 0 ;//用于計(jì)入當(dāng)前字符串?dāng)?shù)組的位數(shù) system.out.println(chararray.length); for(int i = 0 ; i < chararray.length ; i++){ if(chararray[i] == '('){ calculate[j++] = "("; }else if(chararray[i] == ')'){ calculate[j++] = ")"; }else if (chararray[i] == '+') { calculate[j++] = "+"; }else if (chararray[i] == '-') { calculate[j++] = "-"; }else if (chararray[i] == '*') { calculate[j++] = "*"; }else if (chararray[i] == '/') { calculate[j++] = "/"; }else if (chararray[i] == '%') { calculate[j++] = "%"; }else if (chararray[i] == '#') { calculate[j++] = "#"; }else { string str=string.valueof(chararray[i]); number = number * 10 + integer.parseint(str);system.out.println("123"); if( (i + 1) == chararray.length || chararray[i+1] < '0' || chararray[i+1] > '9'){ if ( (i + 1) != chararray.length && chararray[i+1] == ' ') { system.out.println("456");i++; } calculate[j++] = string.valueof(number); system.out.println(number); number = 0 ; } } system.out.println("---z->" + calculate[i]); } calculatelength = j-- ;//不--會(huì)將‘#'存入 } public void outputcalculate() { for(int i = 0 ; i < calculatelength ; i ++ ){ system.out.println(calculate[i]); } } public void calculatetozero() { for(int i = 0 ; i < calculatelength ; i ++ ){ calculate[i]= calculate[999] ; } } //中綴轉(zhuǎn)后綴 public void topostfix() { // todo auto-generated method stub system.out.println("789"); int sum = 0 ;//用于記入”（）“總個(gè)數(shù) int j = 0 ;//用于讀到”）“時(shí)循環(huán)出棧 string outstack = null; charnum.push(null); system.out.println(calculatelength); for( int i = 0 ; i < calculatelength ; i ++){ system.out.println(calculate[i]);//----------------------------- if ( calculate[i].equals("(")) { charnum.push(calculate[i]); system.out.println("1-1 charpush " + calculate[i]);//----------------------------- sum ++ ; }else if ( calculate[i].equals(")") ) { system.out.println("2-1 charpush " + calculate[i]);//----------------------------- outstack = charnum.pop();//進(jìn)入前先出一個(gè) system.out.println("2-1 charpush " + outstack);//----------------------------- while ( !outstack.equals("(") ){ system.out.println("2-2 charpush " + outstack);//----------------------------- num.push(outstack); outstack = charnum.pop(); }//最后一次outstack正好接到”（“不入棧 system.out.println("qiangxing 1 = " + outstack );// outstack = charnum.pop(); system.out.println("qiangxing 2 = " + outstack ); sum ++ ; }else if (calculate[i].equals("*")) { outstack = charnum.pop(); charnum.push(outstack); system.out.println("3-2 charpush " + outstack);//----------------------------- while( ( outstack == "*" || outstack == "/" ) && !(outstack == null) ){ system.out.println("3-1 charpush " + outstack);//----------------------------- num.push(outstack); charnum.pop();//由于前第三行又將outstack存入棧中，座椅此處再次彈出 outstack = charnum.pop(); charnum.push(outstack); } system.out.println("3-3 charpush " + outstack);//----------------------------- charnum.push("*"); }else if (calculate[i].equals("/")) { system.out.println("5-1-0 charpush " + "1-1-1-1-1-1-1-1");//----------------------------- outstack = charnum.pop(); system.out.println("5-1-1 charpush " + "2-2-2-2-2-2-22-2");//----------------------------- charnum.push(outstack); system.out.println("4-1 charpush " + outstack);//----------------------------- while( ( outstack == "*" || outstack == "/" ) && !(outstack == null) ){ system.out.println("4-2 charpush " + outstack);//----------------------------- num.push(outstack); charnum.pop();//由于前第三行又將outstack存入棧中，座椅此處再次彈出 outstack = charnum.pop(); charnum.push(outstack); } system.out.println("4-3 charpush " + outstack);//----------------------------- system.out.println("5-1-2 charpush " + outstack);//----------------------------- charnum.push("/"); }else if (calculate[i].equals("+")) { outstack = charnum.pop(); charnum.push(outstack); system.out.println("5-1 charpush " + outstack);//----------------------------- while( !(outstack=="(") && !(outstack == null) ){ system.out.println("5-2 charpush " + outstack);//----------------------------- num.push(outstack); charnum.pop(); outstack = charnum.pop(); charnum.push(outstack); } system.out.println("5-3 charpush " + outstack);//----------------------------- charnum.push("+"); }else if (calculate[i].equals("-")) { outstack = charnum.pop(); charnum.push(outstack); system.out.println("6-1 charpush " + outstack);//----------------------------- while( !(outstack=="(") && !(outstack == null) ){ system.out.println("6-2 charpush " + outstack);//----------------------------- num.push(outstack); charnum.pop(); outstack = charnum.pop(); charnum.push(outstack); } system.out.println("6-3 charpush " + outstack);//----------------------------- charnum.push("-"); }else { system.out.println("7-7 " + calculate[i]); num.push(calculate[i]); } } system.out.println("匹配結(jié)束" + outstack); outstack = charnum.pop(); system.out.println("finish 1 == " + outstack); while ( outstack != null ) { num.push(outstack); outstack = charnum.pop(); system.out.println("finish 2 == " + outstack); } calculatelength = calculatelength - sum ; system.out.println( "0.0.0.0 charpush " );//----------------------------- system.out.println("sum = " + sum + " calculate = " + calculatelength + "calculatelength-sum = " + (calculatelength-sum)); system.out.println("over ~~~~~0 "); stack<string> zanshi = new stack<>();// num.pop(); for(int i = 0 ; i < calculatelength ; i ++ ){ zanshi.push(num.pop());// system.out.println(num.pop()); } calculatetozero(); system.out.println("over ~~~~~1 "); for(int i = 0 ; i < calculatelength ;i ++ ){ calculate[i] = zanshi.pop(); } system.out.println("over ~~~~~2 "); for(int i = 0 ; i < calculatelength ;i ++ ){ system.out.println(calculate[i]); } system.out.println("over ~~~~~3 ");// num.push("#"); } //后綴計(jì)算 public string postfix() { int a = 0 , b = 0;//棧中彈出的兩數(shù) int sum ;//求兩數(shù)運(yùn)算 for (int i = 0; i < calculatelength ; i++ ) {// system.out.println("目前符號(hào)：" + calculate[i]); if (i == 0) { num.push(calculate[i]); }else if (calculate[i].equals("+") ) { b = integer.parseint(num.pop()); a = integer.parseint(num.pop()); sum = a + b ; num.push(string.valueof(sum)); }else if (calculate[i].equals("-") ) { b = integer.parseint(num.pop()); a = integer.parseint(num.pop()); sum = a - b ; num.push(string.valueof(sum)); }else if (calculate[i].equals("*") ) { b = integer.parseint(num.pop()); a = integer.parseint(num.pop()); sum = a * b ; num.push(string.valueof(sum)); }else if (calculate[i].equals("/") ) { b = integer.parseint(num.pop()); a = integer.parseint(num.pop()); sum = a / b ; num.push(string.valueof(sum)); }else if (calculate[i].equals("%") ) { b = integer.parseint(num.pop()); a = integer.parseint(num.pop()); sum = a / b ; num.push(string.valueof(sum)); }else { num.push(calculate[i]); } } return num.pop(); }} |
結(jié)果如下：
一、前綴轉(zhuǎn)后綴并輸出
其中over前為轉(zhuǎn)化后的后綴表達(dá)式
over后為計(jì)算結(jié)果
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public class main { public static void main(string[] args) { text text = new text(); text.tostringarray("1+2*(3-1+2)-3"); text.outputcalculate(); text.topostfix(); system.out.println(text.postfix()); }} |
二、后綴直接輸出
注意后綴表達(dá)式時(shí)
為了實(shí)現(xiàn)多位數(shù)運(yùn)算，連續(xù)輸入一串?dāng)?shù)時(shí) ，輸入完一個(gè)數(shù)加空格
如：要計(jì)算："1+2*(3-1+2)-3" 則輸入："1 2 3 1-2+*+3-"
例：
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public class main { public static void main(string[] args) { text text = new text(); text.tostringarray("1 2 3 1-2+*+3-"); text.outputcalculate(); system.out.println(text.postfix()); }} |
輸出結(jié)果：
以上就是本文的全部?jī)?nèi)容，希望對(duì)大家的學(xué)習(xí)有所幫助，也希望大家多多支持服務(wù)器之家。
原文鏈接：https://blog.csdn.net/qq_43377749/article/details/84483862
