解题思路
还是用栈
提交代码
class Solution {
public int calculate(String s) {
int res=0,p=0,num=0,tmp=0,flag=1;
Stack<Integer> stack=new Stack<Integer>();
while(p<s.length()) {
if(s.charAt(p)>='0'&&s.charAt(p)<='9') {
num=s.charAt(p)-'0';
while(p+1<s.length()&&s.charAt(p+1)>='0'&&s.charAt(p)<='9') {
num*=10;
num+=s.charAt(p+1)-'0';
p++;
}
stack.push(flag*num);
flag=1;
}else if(s.charAt(p)=='-') {
flag=-1;
}else if(s.charAt(p)=='*') {
while(s.charAt(p+1)==' ') p++;
tmp=s.charAt(++p)-'0';
while(p+1<s.length()&&s.charAt(p+1)>='0'&&s.charAt(p+1)<='9') {
tmp*=10;
tmp+=s.charAt(++p)-'0';
}
res=stack.pop()*tmp;
stack.push(res);
}else if(s.charAt(p)=='/') {
while(s.charAt(p+1)==' ') p++;
tmp=s.charAt(++p)-'0';
while(p+1<s.length()&&s.charAt(p+1)>='0'&&s.charAt(p+1)<='9') {
tmp*=10;
tmp+=s.charAt(++p)-'0';
}
res=stack.pop()/tmp;
stack.push(res);
}
p++;
}
res=0;
while(!stack.isEmpty())
res+=stack.pop();
return res;
}
}