添加（0121.买卖股票的最佳时机.md）：增加typescript版本

problems/0121.买卖股票的最佳时机.md

@@ -426,6 +426,46 @@ var maxProfit = function(prices) {
 };
 ```
 
+TypeScript：
+
+> 贪心法
+
+```typescript
+function maxProfit(prices: number[]): number {
+    if (prices.length === 0) return 0;
+    let buy: number = prices[0];
+    let profitMax: number = 0;
+    for (let i = 1, length = prices.length; i < length; i++) {
+        profitMax = Math.max(profitMax, prices[i] - buy);
+        buy = Math.min(prices[i], buy);
+    }
+    return profitMax;
+};
+```
+
+> 动态规划
+
+```typescript
+function maxProfit(prices: number[]): number {
+    /**
+        dp[i][0]: 第i天持有股票的最大现金
+        dp[i][1]: 第i天不持有股票的最大现金
+     */
+    const length = prices.length;
+    if (length === 0) return 0;
+    const dp: number[][] = [];
+    dp[0] = [-prices[0], 0];
+    for (let i = 1; i < length; i++) {
+        dp[i] = [];
+        dp[i][0] = Math.max(dp[i - 1][0], -prices[i]);
+        dp[i][1] = Math.max(dp[i - 1][0] + prices[i], dp[i - 1][1]);
+    }
+    return dp[length - 1][1];
+};
+```
+
+
+
 
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