Arrays

Coding Problems

Given an array of integers nums and an integer target, return indices of the two numbers such that they add up to target. #leetcode

Time Complexity -O(n^2) - 45ms

public int[] twoSum(int[] nums, int target) {
    for(int i = 0; i < nums.length; i++) {
        for(int j = i + 1; j < nums.length; j++) {
            if(nums[i] + nums[j] == target) {
                return new int[]{i, j};
            }
        }
    }
    return new int[]{};
}

Time Complexity - O(n) - 2ms

public int[] twoSum(int[] nums, int target) {  
    
    Map<Integer, Integer> map = new HashMap<>();  
  
    for (int i = 0; i < nums.length; i++) {  
        int composition_pair = target - nums[i];  
        if (map.containsKey(composition_pair)) {  
            return new int[]{ map.get(composition_pair), i };  
        }  
        map.put(nums[i], i);  
    }  
  
    throw new IllegalArgumentException("No two sum solution found");  
}

You are given an array prices where prices[i] is the price of a given stock on the ith day. You want to maximize your profit by choosing a single day to buy one stock and choosing a different day in the future to sell that stock.Return the maximum profit you can achieve from this transaction. If you cannot achieve any profit, return 0.

Time Complexity - O(n^2)

public int maxProfit(int[] prices) {  
    int maxProfit=0;  
    for (int i = 1; i<prices.length; i++) {  
        for (int j = 0; j < i; j++) {  
            int profit = prices[prices.length - 1-j] - prices[i - 1-j];  
            if (profit > maxProfit) {  
                maxProfit = profit;  
                System.out.println("Selling on Day " + j);  
            }  
        }  
        System.out.println("Buying on Day " + i);  
    }  
  
    return  maxProfit;  
}