add

5.leetcode/src/com/fanxb/common/Q121.java

@@ -0,0 +1,24 @@
+package com.fanxb.common;
+
+/**
+ * 线性扫描，只需找到最大和最小数的差即可，假设第一个数为最小值，从第二个数开始遍历，如果大于最小值则计算利润，如果小于最小值就将最小值设置当前值，然后继续往后便利，知道遍历完毕
+ *
+ * @author FleyX
+ * date 2022/2/23 22:47
+ */
+public class Q121 {
+
+    public int maxProfit(int[] prices) {
+        int max = 0;
+        int minVal = prices[0];
+        for (int i = 1; i < prices.length; i++) {
+            if (prices[i] > minVal) {
+                max = Math.max(max, prices[i] - minVal);
+            } else {
+                minVal = prices[i];
+            }
+        }
+        return max;
+    }
+
+}

5.leetcode/src/com/fanxb/common/Q122.java

@@ -6,9 +6,7 @@ import java.util.List;
 import java.util.Map;
 
 /**
- * 题目地址： https://leetcode-cn.com/problems/partition-labels/
- * 解题思路：首先遍历一次字符串，记录每个字母最后出现的位置
- * 然后再遍历一遍，记录当前字符串的开始位置start,结束位置end. 当第i个字母的结束位置》end时end=第i个字母的结束位置，知道i=end说明当前位置为字符串的结束位置
+ * 找到每次从低点到高点的变化即可
  *
  * @author fanxb
  * Date: 2020/6/9 15:10
@@ -17,25 +15,19 @@ public class Q122 {
 
     public static int solution(int[] prices) {
         int res = 0;
-        int start = -1, end = -1;
+        int start = -1;
         for (int i = 0; i < prices.length - 1; i++) {
-            if (prices[i + 1] > prices[i]) {
-                //说明是上坡
-                if (start == -1) {
-                    start = prices[i];
-                }
-                end = prices[i + 1];
-            } else if (prices[i + 1] < prices[i]) {
-                //说明开始下坡了
-                if (end > start) {
-                    res += end - start;
-                }
+            if (prices[i + 1] > prices[i] && start == -1) {
+                //说明是首次上坡
+                start = prices[i];
+            } else if (prices[i + 1] < prices[i] && start != -1) {
+                res += prices[i] - start;
                 start = -1;
-                end = -1;
             }
         }
-        if (end > start) {
-            res += end - start;
+        //判断最后一个能不能卖
+        if (start != -1 && prices[prices.length - 1] > start) {
+            res += prices[prices.length - 1] - start;
         }
         return res;
     }

5.leetcode/src/com/fanxb/common/Q123.java

@@ -0,0 +1,34 @@
+package com.fanxb.common;
+
+/**
+ * 题目地址： https://leetcode-cn.com/problems/partition-labels/
+ *
+ * @author fanxb
+ * Date: 2020/6/9 15:10
+ */
+public class Q123 {
+
+    public static int solution(int[] prices) {
+        int res = 0;
+        int start = -1;
+        for (int i = 0; i < prices.length - 1; i++) {
+            if (prices[i + 1] > prices[i] && start == -1) {
+                //说明是首次上坡
+                start = prices[i];
+            } else if (prices[i + 1] < prices[i] && start != -1) {
+                res += prices[i] - start;
+                start = -1;
+            }
+        }
+        //判断最后一个能不能卖
+        if (start != -1 && prices[prices.length - 1] > start) {
+            res += prices[prices.length - 1] - start;
+        }
+        return res;
+    }
+
+    public static void main(String[] args) {
+        int[] prices = {7, 1, 5, 3, 6, 4};
+        System.out.println(solution(prices));
+    }
+}