Create: 0838-push-dominoes.js

javascript/0838-push-dominoes.js

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+/**
+ * 838. Push Dominoes
+ * -----------------------
+ * link: https://leetcode.com/problems/push-dominoes/
+ *
+ * description: follow the rules of dominoes falling physics after one sec.
+ *
+ * time: O(n^2)
+ * space: O(n)
+ */
+
+/**
+ * @param {string} dominoes
+ * @return {string}
+ */
+var pushDominoes = function (dominoes) {
+    if (dominoes.length === 1) return dominoes;
+
+    let dominoesArr = [...dominoes];
+
+    for (let i = 0; i < dominoesArr.length; i++) {
+        if (dominoesArr[i] !== '.') continue;
+
+        let [left, right] = nearestMove(dominoesArr, i);
+
+        if (left === -1 && right === -1) continue;
+
+        if (left === -1 && dominoesArr[right] === 'L') {
+            dominoesArr[i] = 'L';
+        } else if (right === -1 && dominoesArr[left] === 'R') {
+            dominoesArr[i] = 'R';
+        } else if (i - left !== right - i) {
+            if (i - left < right - i && dominoesArr[left] === 'R') {
+                dominoesArr[i] = 'R';
+                dominoesArr[right - 1] = dominoesArr[right];
+            } else if (i - left > right - i && dominoesArr[right] === 'L') {
+                dominoesArr[i] = 'L';
+                dominoesArr[left + 1] = dominoesArr[left];
+            } else if (dominoesArr[left] === dominoesArr[right]) {
+                dominoesArr[i] = dominoesArr[right];
+            }
+        } else if (dominoesArr[left] === dominoesArr[right]) {
+            dominoesArr[i] = dominoesArr[right];
+        }
+    }
+
+    return dominoesArr.join('');
+};
+
+/**
+ * @param {string[]} dominoes
+ * @param {number} index
+ * @returns {number[]}
+ */
+var nearestMove = function (dominoes, index) {
+    let ans = [-1, -1];
+
+    for (let i = index - 1; i > -1; i--) {
+        if (ans[0] === -1 && (dominoes[i] === 'L' || dominoes[i] === 'R')) {
+            ans[0] = i;
+            break;
+        }
+    }
+
+    for (let i = index + 1; i < dominoes.length; i++) {
+        if (ans[1] === -1 && (dominoes[i] === 'L' || dominoes[i] === 'R')) {
+            ans[1] = i;
+            break;
+        }
+    }
+
+    return ans;
+};