计算器相关题目总结
选自leetcode basic calculator
Version 1: Support [ + - ]
(not tested)
class Solution {
public int calculate(String s) {
int len = s.length(), sign = 1, res = 0, num = 0;
for (int i = 0; i < len; i++) {
char c = s.charAt(i);
if (c == ' ') continue;
if (Character.isDigit(c)) {
num = num * 10 + c - '0';
if (i == len - 1 || !Character.isDigit(s.charAt(i + 1))) { // 当后一位不是数字时就停止并且reset
res += sign * num;
num = 0;
}
} else { // + or -
if (c == '+') sign = 1; // 记录之前的状态，因为数字是一个位一个位
if (c == '-') sign = -1;
}
}
return res;
}
}
Version 2: Support [ + - ( ) ] (this problem)
class Solution {
public int calculate(String s) {
int len = s.length(), sign = 1, res = 0, num = 0;
Stack<Integer> stack = new Stack<>();
for (int i = 0; i < len; i++) {
char c = s.charAt(i);
if (c == ' ') continue; //只要数字不会被拆开，用这个就没问题。
if (Character.isDigit(c)) {
num = num * 10 + c - '0';
if (i == len - 1 || !Character.isDigit(s.charAt(i + 1))) {
res += sign * num;
num = 0;
}
} else { // + - ( )
if (c == '+') {
sign = 1;
}
if (c == '-') {
sign = -1;
}
if (c == '(') {
stack.push(res);
stack.push(sign);
res = 0;
sign = 1;
}
if (c == ')') {
res = res * stack.pop() + stack.pop(); //现在的和sign+之前的
}
}
}
return res;
}
}
Version 3: Support [ + - * / ]
class Solution {
public int calculate(String s) {
if (s == null || s.length() == 0) return 0;
int len = s.length();
int num = 0;
char sign = '+';
int curr = 0, res = 0; //important, use curr to store value of last segment.
for (int i = 0; i < len; i++) {
if (s.charAt(i) == ' ') continue;
if (!Character.isDigit(s.charAt(i))) {
num = 0;
sign = s.charAt(i);
if (sign == '+' || sign == '-') {
res += curr;
curr = 0; // not necessary
}
} else {
num = num * 10 + s.charAt(i) - '0';
if (i == len - 1 || !Character.isDigit(s.charAt(i + 1))) {
if (sign == '+') curr = num;
if (sign == '-') curr = -num;
if (sign == '*') curr *= num;
if (sign == '/') curr /= num;
}
}
}
res += curr; // add last segment
return res;
}
}
Version 4: Support [ + - * / ( ) ]
Should be easily derived from Version 6, just remove anything related to ^.
Version 5: Support [ + - * / ^ ]
class Solution {
public int calculate(String s) {
// remove spaces //这部分也可以放在下面判断，一句搞定，是空格的时候跳过
String[] strs = s.split(" ");
StringBuilder sb = new StringBuilder();
for (int i = 0; i < strs.length; i++) {
sb.append(strs[i]);
}
s = sb.toString();
// init
if (s == null || sb.length() == 0) return 0;
int num = 0;
Stack<Integer> numStack = new Stack<>();
Stack<Character> opStack = new Stack<>();
Map<Character, Integer> map = new HashMap<>();
map.put('+', 1); map.put('-', 1);
map.put('*', 2); map.put('/', 2);
map.put('^', 3);
for (int i = 0; i < s.length(); i++) {
char c = s.charAt(i);
if (Character.isDigit(c)) {
num = num * 10 + c - '0';
if (i == s.length() - 1 || !Character.isDigit(s.charAt(i + 1))) {
numStack.push(num);
num = 0;
}
} else { // op: + - * / ^
if (opStack.empty() || map.get(c) > map.get(opStack.peek())) {
opStack.push(c);
} else {
while (!opStack.empty() && map.get(c) <= map.get(opStack.peek())) {
helper(numStack, opStack);
}
opStack.push(c);
}
}
}
while (!opStack.empty()) {
helper(numStack, opStack);
}
return numStack.pop();
}
private void helper(Stack<Integer> numStack, Stack<Character> opStack) {
int b = numStack.pop();
int a = numStack.pop();
char op = opStack.pop();
if (op == '+') numStack.push(a + b);
if (op == '-') numStack.push(a - b);
if (op == '*') numStack.push(a * b);
if (op == '/') numStack.push(a / b);
if (op == '^') numStack.push((int)Math.pow(a, b));
}
}
Version 6: Support [ + - * / ^ ( ) ]
class Solution {
public int calculate(String s) {
// remove spaces //这部分也可以放在下面判断，一句搞定，是空格的时候跳过
String[] strs = s.split(" ");
StringBuilder sb = new StringBuilder();
for (int i = 0; i < strs.length; i++) {
sb.append(strs[i]);
}
s = sb.toString();
// init
if (s == null || sb.length() == 0) return 0;
int num = 0;
Stack<Integer> numStack = new Stack<>();
Stack<Character> opStack = new Stack<>();
Map<Character, Integer> map = new HashMap<>();
map.put('+', 1); map.put('-', 1);
map.put('*', 2); map.put('/', 2);
map.put('^', 3);
for (int i = 0; i < s.length(); i++) {
char c = s.charAt(i);
if (Character.isDigit(c)) {
num = num * 10 + c - '0';
if (i == s.length() - 1 || !Character.isDigit(s.charAt(i + 1))) {
numStack.push(num);
num = 0;
}
} else { // op or ()
if (c == '(') {
opStack.push(c);
}
if (c == ')') {
while (!opStack.empty() && opStack.peek() != '(') {
helper(numStack, opStack);
}
opStack.pop(); // pop the '('
}
if (map.containsKey(c)) { // + - * / ^
if (opStack.empty() || opStack.peek() == '(' || map.get(c) > map.get(opStack.peek())) {
opStack.push(c);
} else {
while (!opStack.empty() && opStack.peek() != '(' && map.get(c) <= map.get(opStack.peek())) {
helper(numStack, opStack);
}
opStack.push(c);
}
}
}
}
while (!opStack.empty()) {
helper(numStack, opStack);
}
return numStack.pop();
}
private void helper(Stack<Integer> numStack, Stack<Character> opStack) {
int b = numStack.pop();
int a = numStack.pop();
char op = opStack.pop();
if (op == '+') numStack.push(a + b);
if (op == '-') numStack.push(a - b);
if (op == '*') numStack.push(a * b);
if (op == '/') numStack.push(a / b);
if (op == '^') numStack.push((int)Math.pow(a, b));
}
}
