Max swap

python/problem_670/README.md

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+# 670. Maximum Swap
+
+You are given an integer num. You can swap two digits at most once to get the maximum valued number.
+
+Return the maximum valued number you can get.
+
+
+
+Example 1:
+
+Input: num = 2736
+Output: 7236
+Explanation: Swap the number 2 and the number 7.
+
+Example 2:
+
+Input: num = 9973
+Output: 9973
+Explanation: No swap.
+
+
+
+Constraints:
+
+    0 <= num <= 108

python/problem_670/solution1.py

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+class Solution:
+    def maximumSwap(self, num: int) -> int:
+        # we need to track what is the highest number
+        # from the right of current idx
+
+        # convert the int to str
+        str_num = list(str(num))
+        n = len(str_num)
+
+        max_right_idx = [0] * n
+        # last idx will always be same
+        max_right_idx[n - 1] = n - 1
+
+        for i in range(n - 2, -1, -1):
+            # if the current number is greater than max of the right
+            if str_num[i] > str_num[max_right_idx[i + 1]]:
+                max_right_idx[i] = i
+            # keep the max from right
+            else:
+                max_right_idx[i] = max_right_idx[i + 1]
+
+        # now we go from left to right
+        for j in range(n):
+            if str_num[j] < str_num[max_right_idx[j]]:
+                str_num[j], str_num[max_right_idx[j]] = str_num[max_right_idx[j]], str_num[j]
+                return int("".join(str_num))
+
+        return num