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227.java
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227.java
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/* Base calculator II
* https://leetcode.com/problems/basic-calculator-ii/
*
*/
public class Solution {
public int calculate(String s) {
Deque<Integer> nums = new ArrayDeque();
Deque<Character> ops = new ArrayDeque();
Integer cur = null;
for(int i=0; i< s.length() || cur != null; ++i) {
Character c = i<s.length()? s.charAt(i): null;
if(c!= null && Character.isDigit(c)) {
cur = (cur == null)? c - '0' : cur * 10 + c - '0';
continue;
}
if(cur != null) {
Character l = ops.isEmpty()? null :ops.peekLast();
if(l == null || l == '+' || l == '-')
nums.add(cur);
else {
ops.pollLast();
int pre = nums.pollLast();
if(l == '*')
nums.add(pre * cur);
else
nums.add(pre / cur);
}
cur = null;
}
if(c == null || c == ' ') {
continue;
}
ops.add(c);
}
int pre = nums.pollFirst();
while(!ops.isEmpty()) {
char o = ops.pollFirst();
cur = nums.pollFirst();
if(o == '-')
pre = pre - cur;
else
pre = pre + cur;
}
return pre;
}
}