leetcode/src/main/java/basic/QueueAndStack/NiBoLan.java at master · onelogistics/leetcode · GitHub

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packagebasic.QueueAndStack;

importjava.util.Stack;

publicclassNiBoLan {
publicstaticvoidmain(String[] args) {
Stringstr=newNiBoLan().niBoLan("2-(2-1)+3-(2-10)");
System.out.println(newNiBoLan().calNiBoLan(str));
 }
//后缀表达值计算值
publicintcalNiBoLan(Stringstr) {
Stack<Integer> numStack=newStack<>();
intnum=0;
for (inti=0;i<str.length();i++) {
charc=str.charAt(i);
if(Character.isDigit(c)) {
num=c-'0';
while (i+1<str.length() && str.charAt(i+1)!=' ') {
num=10*num+(str.charAt(i+1)-'0');
i++;
 }
numStack.push(num);
i++;//略过空格
 }else {
intb=numStack.pop();
inta=numStack.pop();
inttmp;
switch (c) {
case'*':
tmp=a*b;
break;
case'/':
tmp=a/b;
break;
case'+':
tmp=a+b;
break;
case'-':
tmp=a-b;
break;
default:
tmp=0;
break;
 }
numStack.push(tmp);
 }
 }
returnnumStack.pop();
 }

/**
 * 中缀表达式转后缀表达式
 * @param str
 * @return
 */
publicStringniBoLan(Stringstr) {
StringBuildersb=newStringBuilder();
Stack<Character> opStack=newStack<>();
for (inti=0;i<str.length();i++) {
charc=str.charAt(i);
if(c==' ') continue;
if(Character.isDigit(c)) {
sb.append(c);
while (i+1<str.length() && Character.isDigit(str.charAt(i+1))) {
sb.append(str.charAt(i+1));
i++;
 }
//数字之间以空格分隔
sb.append(' ');
 }else {
chartmp;
if(c=='(') opStack.push(c);
if(c==')') while ((tmp=opStack.pop())!='(') sb.append(tmp);
if(c=='*' || c=='/' || c=='+' || c=='-') {
//扫描到的运算符优先级大于栈顶，直接压栈。
while (!opStack.isEmpty() && getPriority(c)<=getPriority((opStack.peek()))) {
sb.append(opStack.pop());
 }
opStack.push(c);
 }
 }
 }
while (!opStack.isEmpty()) {
sb.append(opStack.pop());
 }
returnsb.toString();
 }
intgetPriority(charop) {
switch (op) {
case'+':
case'-':
return1;
case'*':
case'/':
return2;
default:
return0;
 }
 }
}