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52 lines
1.6 KiB
Markdown
52 lines
1.6 KiB
Markdown
# [402. Remove K Digits](https://leetcode.com/problems/remove-k-digits/)
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## 题目
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Given a non-negative integer num represented as a string, remove k digits from the number so that the new number is the smallest possible.
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Note:
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- The length of num is less than 10002 and will be ≥ k.
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- The given num does not contain any leading zero.
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Example 1:
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```c
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Input: num = "1432219", k = 3
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Output: "1219"
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Explanation: Remove the three digits 4, 3, and 2 to form the new number 1219 which is the smallest.
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```
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Example 2:
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```c
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Input: num = "10200", k = 1
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Output: "200"
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Explanation: Remove the leading 1 and the number is 200. Note that the output must not contain leading zeroes.
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```
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Example 3:
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```c
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Input: num = "10", k = 2
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Output: "0"
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Explanation: Remove all the digits from the number and it is left with nothing which is 0.
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```
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## 题目大意
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给定一个以字符串表示的非负整数 num，移除这个数中的 k 位数字，使得剩下的数字最小。
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注意:
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- num 的长度小于 10002 且 ≥ k。
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- num 不会包含任何前导零。
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## 解题思路
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从开头扫 num 每一位，依次入栈，当新来的数字比栈顶元素小，就依次往前移除掉所有比这个新来数字大的数字。注意最后要求剩下的数字最小，如果最后剩下的数字超过了 K 位，取前 K 位必然是最小的(因为如果后 K 位有比前 K 位更小的值的话，会把前面大的数字踢除的)
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注意，虽然 num 不会包含前导 0，但是最终删掉中间的数字以后，比如删掉 0 前面的所有数字以后，前导 0 就会出来，最终输出的时候要去掉前导 0 。
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