好！maximum-product-of-word-lengths

以后看到个数比较少,性能比较高,就要第一时间想到位操作!

这道题目mock没有通过。超时了。。。。。。

原来题目解法的思路非常非常好！

开始我关注于降低n*n的复杂度,但是这道题目复杂度高在每个字符串长,所以一定要问清楚题目

新做的记录：

package com.company;

import java.util.*;
import java.util.List;

class Solution {
    public int maxProduct(String[] words) {
        // int是32位,足够处理了。真的很牛逼
        // 以后看到个数比较少,性能比较高,就要第一时间想到位操作!
        // 开始我关注于降低n*n的复杂度,但是这道题目复杂度高在每个字符串长,所以一定要问清楚题目
        List<Integer> ilist = new ArrayList<>();
        for (int i=0; i<words.length; i++) {
            int nb = 0;
            for (int j=0; j<words[i].length(); j++) {
                nb |= 1 << (words[i].charAt(j) - ‘a‘);
            }
            ilist.add(nb);
        }
        int ret = 0;
        for (int i=0; i<words.length; i++) {
            for (int j=i+1; j<words.length; j++) {
                if ((ilist.get(i) & ilist.get(j)) == 0) {
                    if (words[i].length() * words[j].length() > ret) {
                        ret = words[i].length() * words[j].length();
                    }
                }
            }
        }
        return ret;
    }
}

public class Main {

    public static void main(String[] args) {
        // write your code here
        System.out.println("Hello");
        Solution solution = new Solution();

        String[] words= {"cdea","bdd"};
        int ret = solution.maxProduct(words);
        System.out.printf("Get ret: %d\n", ret);

    }
}

原来做过的记录

https://leetcode.com/problems/maximum-product-of-word-lengths/

// 我在尽量做到比n*n效率更高
// 对比new solution和previous solution
// new solution 是纯n*n，优化在字符串比较
// 对于大数据，耗时0ms
// previous solution理论上比n*n要快，
// 但是因为涉及vector的频繁增删、复制
// 实际要慢的多，对于大数据耗时800+ms

// 总的来看，stl container的复制、删除等，耗时很大

class Solution {
    vector<pair<int, int>> vec;
    vector<string> words;
    int **DP;
    // 比较的好方法
    int *bits;

    static bool my_compair(const string &a, const string &b) {
        if (a.size() > b.size()) {
            return true;
        }
        else {
            return false;
        }
    }

    void insert(int i, int j) {
        int f = words[i].size() * words[j].size();

        int vlen = vec.size();
        int begin = 0;
        int end = vlen - 1;

        int mid;
        int tmp;
        while (begin <= end) {
            mid = (begin + end) / 2;
            tmp = words[vec[mid].first].size() * words[vec[mid].second].size();

            if (f == tmp) {
                begin = mid + 1;
                break;
            }
            else if (f > tmp) {
                end = mid - 1;
            }
            else {
                begin = mid + 1;
            }
        }
        vec.insert(vec.begin()+begin, make_pair(i, j));
    }

    int valid(int i, int j) {
        if ((bits[i] & bits[j]) != 0) {
            return 0;
        }
        return words[i].size() * words[j].size();
    }

public:
    int maxProduct(vector<string>& w) {
        words = w;

        int wlen = words.size();
        if (wlen == 0) {
            return 0;
        }
        sort(words.begin(), words.end(), my_compair);

        // 初始化bits
        bits = new int[wlen];
        memset(bits, 0, sizeof(int)*wlen);
        for (int i=0; i<wlen; i++) {
            string wstr = words[i];
            int slen = wstr.size();
            for (int j=0; j<slen; j++) {
                bits[i] |= 1 << (wstr[j]-‘a‘);
            }
        }

        // new solution(0 ms for big test case)
        int result = 0;
        for (int i=0; i<wlen-1; i++) {
            for (int j=i+1; j<wlen; j++) {
                if ((bits[i]&bits[j]) == 0) {
                    int tmp = words[i].size() * words[j].size();
                    if (tmp > result) {
                        result = tmp;
                    }
                }
            }
        }
        return result;

        // previous solution (800ms for big test case)
        DP = new int*[wlen];
        for (int i=0; i<wlen; i++) {
            DP[i] = new int[wlen];
            // 注意，new出来的数据初始值，不一定为0
            memset(DP[i], 0, sizeof(int)*wlen);
        }

        // 根据相乘的长度排序
        vec.push_back(make_pair(0, 1));
        DP[0][1] = 1;

        int fir;
        int sec;
        int tmp;

        while (!vec.empty()) {
            fir = vec[0].first;
            sec = vec[0].second;
            vec.erase(vec.begin());

            tmp = valid(fir, sec);
            if (tmp > result) {
                result = tmp;
            }

            if (fir + 1 < sec && DP[fir+1][sec] == 0 &&
                words[fir+1].size() * words[sec].size() > result) {
                insert(fir+1, sec);
                DP[fir+1][sec] = 1;
            }
            if (sec + 1 < wlen && DP[fir][sec+1] == 0 &&
                words[fir].size() * words[sec+1].size() > result) {
                insert(fir, sec+1);
                DP[fir][sec+1] = 1;
            }
        }
        return result;
    }
};

// 下面是我在 Mock里面做的，超时了。重来。
package com.company;

import java.awt.*;
import java.util.*;
import java.util.List;

class Solution {
    public int maxProduct(String[] words) {
        // 直接用n*n*size的方法肯定不好
        // 注意限制条件, lower case的字符

        Map<Integer, Set<Integer>> mp = new HashMap<>();

        List<Integer> clist = new ArrayList<>();

        for (int i=0; i<words.length; i++) {
            clist.add(i);

            // 过滤
            char[] chs = words[i].toCharArray();
            Set<Integer> wSet = new HashSet();
            for (char ch :chs) {
                wSet.add(ch - ‘a‘);
            }
            Iterator<Integer> iter = wSet.iterator();
            while (iter.hasNext()) {
                int key = iter.next();
                if (!mp.containsKey(key)) {
                    Set<Integer> st = new HashSet<>();
                    st.add(i);
                    mp.put(key, st);
                }
                else {
                    Set<Integer> st = mp.get(key);
                    st.add(i);
                    mp.put(key, st);
                }
            }

        }

        int ret = 0;
        for (int i=0; i<words.length; i++) {
            Set<Integer> oSet = new HashSet<>(clist);
            char[] chs = words[i].toCharArray();
            Set<Integer> wSet = new HashSet();
            for (char ch :chs) {
                wSet.add(ch - ‘a‘);
            }
            Iterator<Integer> iter = wSet.iterator();
            while (iter.hasNext()) {
                int key = iter.next();
                Set<Integer> st = mp.get(key);
                oSet.removeAll(st);
            }
            iter = oSet.iterator();
            while (iter.hasNext()) {
                int index = iter.next();
                if (words[i].length() * words[index].length() > ret) {
                    ret = words[i].length() * words[index].length();
                }
            }
        }
        return ret;

    }
}

public class Main {

    public static void main(String[] args) {
        // write your code here
        System.out.println("Hello");
        Solution solution = new Solution();

        String[] words= {};
        int ret = solution.maxProduct(words);
        System.out.printf("Get ret: %d\n", ret);

    }
}