update: 316

Author: hijiangtao

README.md

@@ -135,6 +135,7 @@ This is the solutions collection of my LeetCode submissions, most of them are pr
 | 309 | [Best Time to Buy and Sell Stock with Cooldown](https://leetcode.com/problems/best-time-to-buy-and-sell-stock-with-cooldown/)                   | [JavaScript](./src/best-time-to-buy-and-sell-stock-with-cooldown/res.js)                                          | Medium     |
 | 310 | [Minimum Height Trees](https://leetcode.com/problems/minimum-height-trees/)                                                                     | [JavaScript](./src/minimum-height-trees/res.js)                                                                   | Medium     |
 | 315 | [Count of Smaller Numbers After Self](https://leetcode.com/problems/count-of-smaller-numbers-after-self/) <sup>*</sup>                          | [JavaScript](./src/count-of-smaller-numbers-after-self/res.js)                                                    | Hard       |
+| 316 | [remove-duplicate-letters](https://leetcode.com/problems/remove-duplicate-letters/)                                                             | [TypeScript](./src/remove-duplicate-letters/res.ts)                                                               | Medium     |
 | 322 | [Coin Change](https://leetcode.com/problems/coin-change/)                                                                                       | [JavaScript](./src/coin-change/res.js)                                                                            | Medium     |
 | 327 | [Count of Range Sum](https://leetcode.com/problems/count-of-range-sum/)                                                                         | [JavaScript](./src/count-of-range-sum/res.js)                                                                     | Hard       |
 | 334 | [Increasing Triplet Subsequence](https://leetcode.com/problems/increasing-triplet-subsequence/)                                                 | [JavaScript](./src/increasing-triplet-subsequence/res.js)                                                         | Medium     |

src/remove-duplicate-letters/res.ts

@@ -0,0 +1,51 @@
+function removeDuplicateLetters(s: string): string {
+    if (s.length <= 1) {
+        return s;
+    }
+
+    const sList = s.split('');
+    const sCountMap: { [key in string]: number } = {};
+    sList.map(str => {
+        sCountMap[str] = sCountMap[str] ? sCountMap[str]+1 : 1;
+    });
+
+    const remainCountMap: { [key in string]: number } = JSON.parse(JSON.stringify(sCountMap));
+    const resultCountMap: { [key in string]: number } = {};
+
+    Object.keys(sCountMap).forEach(key => resultCountMap[key] = 0);
+    const sStack = [sList[0]];
+    resultCountMap[sList[0]] = 1;
+    remainCountMap[sList[0]] -= 1;
+
+    for (let i = 1; i < sList.length; i++) {
+        const element = sList[i];
+        const prevElement = sStack[sStack.length-1];
+        if (!resultCountMap[element] && element > prevElement) {
+            sStack.push(element);
+            remainCountMap[element] -= 1;
+            resultCountMap[element] = 1;
+        } else if (!resultCountMap[element] && element < prevElement) {
+            let currentIndex = sStack.length-1;
+            while(currentIndex >= 0) {
+                const currentPrevElement = sStack[currentIndex];
+                if (currentPrevElement > element && remainCountMap[currentPrevElement]) {
+                    currentIndex--;
+                } else {
+                    break;
+                }
+            }
+            const sStackLength = sStack.length;
+            for (let j = currentIndex+1; j < sStackLength; j++) {
+                const minusElement = sStack.pop() as string;
+                resultCountMap[minusElement]--;
+            }
+            sStack.push(element);
+            remainCountMap[element]--;
+            resultCountMap[element]++;
+        } else {
+            remainCountMap[element]--;
+        }
+    }
+
+    return sStack.join('');
+};