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MapSumPairs.java
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MapSumPairs.java
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package Leetcode;
/**
* @author kalpak
*
* Implement the MapSum class:
*
* MapSum() Initializes the MapSum object.
* void insert(String key, int val) Inserts the key-val pair into the map. If the key already existed, the original key-value pair will be overridden to the new one.
* int sum(string prefix) Returns the sum of all the pairs' value whose key starts with the prefix.
*
*
* Example 1:
*
* Input
* ["MapSum", "insert", "sum", "insert", "sum"]
* [[], ["apple", 3], ["ap"], ["app", 2], ["ap"]]
* Output
* [null, null, 3, null, 5]
*
* Explanation
* MapSum mapSum = new MapSum();
* mapSum.insert("apple", 3);
* mapSum.sum("ap"); // return 3 (apple = 3)
* mapSum.insert("app", 2);
* mapSum.sum("ap"); // return 5 (apple + app = 3 + 2 = 5)
*
*
* Constraints:
*
* 1 <= key.length, prefix.length <= 50
* key and prefix consist of only lowercase English letters.
* 1 <= val <= 1000
* At most 50 calls will be made to insert and sum.
*
*/
public class MapSumPairs {
TrieNode root;
/** Initialize your data structure here. */
public MapSumPairs() {
root = new TrieNode('\0');
}
public void insert(String key, int val) {
TrieNode current = root;
for (char c : key.toCharArray()) {
if(current.children[c-'a'] == null)
current.children[c-'a'] = new TrieNode(c);
current = current.children[c-'a'];
}
current.val = val;
}
public int sum(String prefix) {
TrieNode current = root;
for (char c : prefix.toCharArray()) {
if(current.children[c-'a'] == null)
return 0;
current = current.children[c-'a'];
}
return getSumDFS(current);
}
private int getSumDFS(TrieNode node) {
int sum = 0;
for (char c = 'a'; c <= 'z'; c++) {
if(node.children[c-'a'] != null) {
sum += getSumDFS(node.children[c-'a']);
}
}
return sum + node.val;
}
class TrieNode {
private char letter;
private TrieNode[] children;
private int val;
public TrieNode(char letter) {
this.letter = letter;
this.children = new TrieNode[26];
this.val = 0;
}
}
}