[Sehwan] Week11 solution with JavaScript

Author: nhistory

coin-change/nhistory.js

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+/**
+ * @param {number[]} coins
+ * @param {number} amount
+ * @return {number}
+ */
+var coinChange = function (coins, amount) {
+  const dp = new Array(amount + 1).fill(amount + 1);
+  dp[0] = 0;
+
+  for (let i = 0; i <= amount; i++) {
+    for (let coin of coins) {
+      if (coin <= i) dp[i] = Math.min(dp[i - coin] + 1, dp[i]);
+    }
+  }
+
+  return dp[amount] < amount + 1 ? dp[amount] : -1;
+};
+
+// TC: O(amount*coins.length)
+// SC: O(amount)

decode-ways/nhistory.js

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+/**
+ * @param {string} s
+ * @return {number}
+ */
+var numDecodings = function (s) {
+  // Edge case
+  if (s.length === 0 || s[0] === "0") return 0;
+
+  let dp = new Array(s.length + 1).fill(0);
+
+  dp[0] = 1;
+  dp[1] = 1;
+
+  for (let i = 2; i <= s.length; i++) {
+    let single = s[i - 1];
+    let double = s[i - 2] + s[i - 1];
+
+    if (single >= 1 && single <= 9) dp[i] += dp[i - 1];
+    if (double >= 10 && double <= 26) dp[i] += dp[i - 2];
+  }
+
+  return dp[s.length];
+};
+
+// TC: O(n)
+// SC: O(n)

maximum-product-subarray/nhistory.js

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+var maxProduct = function (nums) {
+  let result = nums[0];
+  let max = 1,
+    min = 1;
+
+  for (let num of nums) {
+    const candidates = [min * num, max * num, num];
+    min = Math.min(...candidates);
+    max = Math.max(...candidates);
+    result = Math.max(max, result);
+  }
+  return result;
+};
+
+// TC: O(n)
+// SC: O(1)

palindromic-substrings/nhistory.js

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+var countSubstrings = function (s) {
+  let count = 0;
+
+  const isPalindrom = (start, end) => {
+    while (start >= 0 && end < s.length && s[start] === s[end]) {
+      start--;
+      end++;
+      count++;
+    }
+  };
+
+  for (let i = 0; i < s.length; i++) {
+    isPalindrom(i, i); // odd number of str
+    isPalindrom(i, i + 1); // even number of str
+  }
+  return count;
+};
+
+// TC: O(n^2)
+// SC: O(1)

word-break/nhistory.js

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+var wordBreak = function (s, wordDict) {
+  let memo = {};
+
+  const dfs = (start) => {
+    if (start in memo) return memo[start];
+
+    if (start === s.length) {
+      memo[start] = true;
+      return true;
+    }
+
+    for (let word of wordDict) {
+      if (s.substring(start, start + word.length) === word) {
+        if (dfs(start + word.length)) {
+          memo[start] = true;
+          return true;
+        }
+      }
+    }
+    memo[start] = false;
+    return false;
+  };
+
+  return dfs(0);
+};
+
+// n = s.length | m = wordDict.length | L = maximum length of word in wordDict
+// TC: O(n*m*L)
+// SC: O(n)