g0201_0300.s0241_different_ways_to_add_parentheses.Solution Maven / Gradle / Ivy

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Java-based LeetCode algorithm problem solutions, regularly updated

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package g0201_0300.s0241_different_ways_to_add_parentheses;

// #Medium #String #Dynamic_Programming #Math #Recursion #Memoization
// #2022_07_05_Time_3_ms_(70.81%)_Space_42.5_MB_(73.65%)

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class Solution {
    public List diffWaysToCompute(String expression) {
        return diffWaysToCompute(expression, new HashMap<>());
    }

    private List diffWaysToCompute(String expression, Map> map) {
        if (map.containsKey(expression)) {
            return map.get(expression);
        }
        List values = new ArrayList<>();
        if (!hasOperator(expression)) {
            // base case
            values.add(Integer.parseInt(expression));
        } else {
            // Recursive case. DFS
            for (int i = 0; i < expression.length(); i++) {
                char symbol = expression.charAt(i);

                if (!Character.isDigit(symbol)) {
                    List left = diffWaysToCompute(expression.substring(0, i), map);
                    List right = diffWaysToCompute(expression.substring(i + 1), map);
                    for (Integer l : left) {
                        for (Integer r : right) {
                            switch (symbol) {
                                case '+':
                                    values.add(l + r);
                                    break;
                                case '-':
                                    values.add(l - r);
                                    break;
                                case '*':
                                    values.add(l * r);
                                    break;
                                default:
                                    break;
                            }
                        }
                    }
                }
            }
        }
        map.put(expression, values);
        return values;
    }

    private boolean hasOperator(String expression) {
        for (int i = 0; i < expression.length(); i++) {
            switch (expression.charAt(i)) {
                case '+':
                case '-':
                case '*':
                    return true;
                default:
                    break;
            }
        }
        return false;
    }
}