[leetcode]Different Ways to Add Parentheses

最新推荐文章于 2020-05-29 07:21:21 发布

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本文探讨了如何解析包含加、减、乘运算符的字符串，并计算所有可能的组合结果，通过递归方法实现不同分组的计算。

from：https://leetcode.com/submissions/detail/36926833/

Given a string of numbers and operators, return all possible results from computing all the different possible ways to group numbers and operators. The valid operators are+, - and *.

Example 1

Input: "2-1-1".

((2-1)-1) = 0
(2-(1-1)) = 2

Output: [0, 2]

Example 2

Input: "2*3-4*5"

(2*(3-(4*5))) = -34
((2*3)-(4*5)) = -14
((2*(3-4))*5) = -10
(2*((3-4)*5)) = -10
(((2*3)-4)*5) = 10

Output: [-34, -14, -10, -10, 10]

public class Solution {
    Map<String, List<Integer>> subs;
    public List<Integer> diffWaysToCompute(String input) {
        if(null == input || "".equals(input)) return new ArrayList<Integer>();
        
        List<Integer> nums = new ArrayList<Integer>();
        List<Character> opts = new ArrayList<Character>();
        subs = new HashMap<String, List<Integer>>();
        // +:<0    -:=0     *>0
        findOutNumsOpts(input, nums, opts);
        return calculate(nums, opts);
    }
    
    private List<Integer> calculate(List<Integer> nums, List<Character> opts) {
        return calculate(nums, opts, 0, nums.size()-1);
    }
    
    private List<Integer> calculate(List<Integer> nums, List<Character> opts, int st, int ed) {
        List<Integer> anses = new ArrayList<Integer>();
        if(st == ed) {
            anses.add(nums.get(st));
            return anses;
        }
        for(int i=st; i<ed; ++i) {
            List<Integer> lefts = subs.get(st + "-" +i);
            if(null == lefts) {
            	lefts = calculate(nums, opts, st, i);
            	subs.put(st + "-" +i, lefts);
            }
            List<Integer> rigts = subs.get((i+1) + "-" + ed); 
            if(null == rigts) {
            	rigts = calculate(nums, opts, i+1,  ed);
            	subs.put((i+1) + "-" + ed, rigts);            	
            }
            for(Integer lv : lefts) {
                for(Integer rv : rigts) {
                    switch(opts.get(i)) {
                        case '+' : {
                            anses.add(lv+rv);
                            break;
                        }
                        case '-' : {
                            anses.add(lv-rv);
                            break;
                        }
                        case '*' : {
                            anses.add(lv*rv);
                            break;
                        }
                    }
                }
            }
        }
        return anses;
    }
    
    private void findOutNumsOpts(String s, List<Integer> nums, List<Character> opts) {
        for(int i=0, n=s.length(); i<n; ++i) {
            char c = s.charAt(i);
            if('+' == c) {
                opts.add('+');
            } else if('-' == c){
                opts.add('-');
            } else if('*' == c) {
                opts.add('*');
            } else if('0'<=c && '9'>=c) {
                int u = 0;
                while(i<n && '0'<=c && '9'>=c) {
                    u = u*10 + c-'0';
                    ++i;
                    if(i < n) c = s.charAt(i);
                }
                nums.add(u);
                --i;
            }
        }
    }
}

public class Solution {
    public List<Integer> diffWaysToCompute(String input) {
        if(null == input || "".equals(input)) return new ArrayList<Integer>();
        
        List<Integer> nums = new ArrayList<Integer>();
        List<Character> opts = new ArrayList<Character>();
        // +:<0    -:=0     *>0
        findOutNumsOpts(input, nums, opts);
        return calculate(nums, opts);
    }
    
    private List<Integer> calculate(List<Integer> nums, List<Character> opts) {
        return calculate(nums, opts, 0, nums.size()-1);
    }
    
    private List<Integer> calculate(List<Integer> nums, List<Character> opts, int st, int ed) {
        List<Integer> anses = new ArrayList<Integer>();
        if(st == ed) {
            anses.add(nums.get(st));
            return anses;
        }
        for(int i=st; i<ed; ++i) {
            List<Integer> lefts = calculate(nums, opts, st, i);
            List<Integer> rigts = calculate(nums, opts, i+1,  ed);
            for(Integer lv : lefts) {
                for(Integer rv : rigts) {
                    switch(opts.get(i)) {
                        case '+' : {
                            anses.add(lv+rv);
                            break;
                        }
                        case '-' : {
                            anses.add(lv-rv);
                            break;
                        }
                        case '*' : {
                            anses.add(lv*rv);
                            break;
                        }
                    }
                }
            }
        }
        return anses;
    }
    
    private void findOutNumsOpts(String s, List<Integer> nums, List<Character> opts) {
        for(int i=0, n=s.length(); i<n; ++i) {
            char c = s.charAt(i);
            if('+' == c) {
                opts.add('+');
            } else if('-' == c){
                opts.add('-');
            } else if('*' == c) {
                opts.add('*');
            } else if('0'<=c && '9'>=c) {
                int u = 0;
                while(i<n && '0'<=c && '9'>=c) {
                    u = u*10 + c-'0';
                    ++i;
                    if(i < n) c = s.charAt(i);
                }
                nums.add(u);
                --i;
            }
        }
    }
}