코딩공부

※Recursion /** * Definition for singly-linked list. * public class ListNode { * int val; * ListNode next; * ListNode() {} * ListNode(int val) { this.val = val; } * ListNode(int val, ListNode next) { this.val = val; this.next = next; } * } */ class Solution { public ListNode mergeTwoLists(ListNode list1, ListNode list2) { if(list1 == null) return list2; if(list2 == null) return list1; if(list1.va..

import java.util.Stack; class Valid_Parantheses { public boolean isValid(String s) { Stackstack = new Stack(); for(char c : s.toCharArray()){ if(c == '('){ stack.push(')'); }else if(c == '['){ stack.push(']'); }else if(c == '{'){ stack.push('}'); }else if(stack.isEmpty() || stack.pop()!= c){ return false; } } return stack.isEmpty(); } } ※ toCharArray() : The Java string toCharArray() method conv..

public class TwoSum_1 { public int[] twoSum(int[] nums, int target) { int length = nums.length; for(int i = 0; i < length; i++){ int diff = target - nums[i]; for(int j = i+1; j < length; j++){ if(diff == nums[j]){ return new int[]{i,j}; } } } return new int[]{0,0}; } } First approach: HashMap 쓰지 않고, for loop 사용 run time = 60ms import java.util.HashMap; class Solution { public int[] twoSum(int[] ..