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)); } }