677. Map Sum Pairs(JAVA)

題目

Implement a MapSum class with insert, and sum methods.

For the method insert, you'll be given a pair of (string, integer). The string represents the key and the integer represents the value. If the key already existed, then the original key-value pair will be overridden to the new one.

For the method sum, you'll be given a string representing the prefix, and you need to return the sum of all the pairs' value whose key starts with the prefix.

Example 1:

Input: insert("apple", 3), Output: NullInput: sum("ap"), Output: 3Input: insert("app", 2), Output: NullInput: sum("ap"), Output: 5

解題思路

把map組放進vector裏。每次放入前先檢查string是否相同，若相同則修改其num數值，若沒有相同則push新數據。查找則檢查是否存在子串(不存在返回-1)以及子串是否為前綴(若不為前綴返回值大於0)，把所有符合條件的num相加即為返回值。

代碼

import java.util.*;


class MapSum {
    
    Vector<MyMap> map;


    /** Initialize your data structure here. */
    public MapSum() {
        map = new Vector<MyMap>();
    }
    
    public void insert(String key, int val) {
        int i;
        for (i = 0; i < map.size(); i++) {
            if (map.get(i).str.equals(key)) {
                map.get(i).num = val;
                break;
            }
        }
        if (i == map.size()) {
            MyMap m = new MyMap(key,val);
            map.add(m);
        }


    }
    
    public int sum(String prefix) {
        int sum = 0;
        for (int i = 0; i < map.size(); i++) {
            if (map.get(i).str.indexOf(prefix) == 0) {
                sum += map.get(i).num;
            }
        }
        return sum;
    }
}


class MyMap {
    public String str;
    public int num;
    
    public MyMap(String string, int n) {
        str = string;
        num = n;
    }
}

感想

沒甚麼難度的一道，注意題目條件即可。