Add week 1 solutions

Author: yolophg

best-time-to-buy-and-sell-stock/yolophg.js

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+var maxProfit = function(prices) {
+    let lowBuy = prices[0];
+    let profit = 0;
+    // loop over the array
+    for(let i = 0; i < prices.length; i++) {
+        // to set lowBuy to adjust as lower numbers 
+        if ( prices[i] < lowBuy ) {
+            lowBuy = prices[i];
+        } 
+        // check the subtract current iteration on array - lowBuy price to calculate current profit
+        if ( prices[i] - lowBuy > profit) {
+            profit = prices[i] - lowBuy ;
+        }
+    }
+    return profit;
+};

contains-duplicate/yolophg.js

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+var containsDuplicate = function(nums) {
+    let set = new Set([nums[0]]);
+
+    // check if the current value is in the set
+    for(let i = 1; i < nums.length; i++){
+        // if it's already in the set, return true
+        if(set.has(nums[i])){
+            return true;
+        // if it's not in the set, add it to set and resume 
+        } else {
+            set.add(nums[i]);
+        }
+    }
+    return false;
+};

two-sum/yolophg.js

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+var twoSum = function(nums, target) {
+    const hash = new Map();
+    
+    for( let i = 0 ; i < nums.length; i++) {
+        // find num to make a target
+        const findTarget = target - nums[i];
+
+        // if find num, return
+        if(hash.get(findTarget) !== undefined)  return [hash.get(findTarget), i];
+        
+        // if couldn't find, set in the map
+        hash.set(nums[i], i);
+    }
+    
+    return [];
+};

valid-anagram/yolophg.js

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+var isAnagram = function(s, t) {
+    firstList = s.split("").sort();
+    secondList = t.split("").sort();
+
+    // compare if these are same and return
+    return JSON.stringify(firstList) === JSON.stringify(secondList);
+};

valid-palindrome/yolophg.js

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+var isPalindrome = function(s) {
+    let regex = /[!"#$%&'()*+,-./:;<=>?@[\]^_`{|}~"" ]/g;
+    let convertToLowerCase = s.replace(regex, '').toLowerCase();
+    let middleOftheString = parseInt(convertToLowerCase.length / 2);
+    let result;
+
+    // iterate over each value of string till to reache the middle of the string
+    for (let i = 0; i <= middleOftheString; i++) {
+        // check if values match
+        if (convertToLowerCase[i] === convertToLowerCase[convertToLowerCase.length - 1 - i]) {
+            result = true;
+        // if there's nothing else to check for, return false and break the loop
+        } else {
+            result = false;
+            break;
+        }
+    }
+    return result;    
+};