README_EN.md

316. Remove Duplicate Letters

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Description

Given a string s, remove duplicate letters so that every letter appears once and only once. You must make sure your result is the smallest in lexicographical order among all possible results.

 

Example 1:

Input: s = "bcabc"
Output: "abc"

Example 2:

Input: s = "cbacdcbc"
Output: "acdb"

 

Constraints:

• 1 <= s.length <= 104
• s consists of lowercase English letters.

 

Note: This question is the same as 1081: https://leetcode.com/problems/smallest-subsequence-of-distinct-characters/

Solutions

Stack

Python3

class Solution:
    def removeDuplicateLetters(self, s: str) -> str:
        last = {c: i for i, c in enumerate(s)}
        stk = []
        vis = set()
        for i, c in enumerate(s):
            if c in vis:
                continue
            while stk and stk[-1] > c and last[stk[-1]] > i:
                vis.remove(stk.pop())
            stk.append(c)
            vis.add(c)
        return ''.join(stk)

class Solution:
    def removeDuplicateLetters(self, s: str) -> str:
        count, in_stack = [0] * 128, [False] * 128
        stack = []
        for c in s:
            count[ord(c)] += 1
        for c in s:
            count[ord(c)] -= 1
            if in_stack[ord(c)]:
                continue
            while len(stack) and stack[-1] > c:
                peek = stack[-1]
                if count[ord(peek)] < 1:
                    break
                in_stack[ord(peek)] = False
                stack.pop()
            stack.append(c)
            in_stack[ord(c)] = True
        return ''.join(stack)

Java

class Solution {
    public String removeDuplicateLetters(String s) {
        int n = s.length();
        int[] last = new int[26];
        for (int i = 0; i < n; ++i) {
            last[s.charAt(i) - 'a'] = i;
        }
        Deque<Character> stk = new ArrayDeque<>();
        int mask = 0;
        for (int i = 0; i < n; ++i) {
            char c = s.charAt(i);
            if (((mask >> (c - 'a')) & 1) == 1) {
                continue;
            }
            while (!stk.isEmpty() && stk.peek() > c && last[stk.peek() - 'a'] > i) {
                mask ^= 1 << (stk.pop() - 'a');
            }
            stk.push(c);
            mask |= 1 << (c - 'a');
        }
        StringBuilder ans = new StringBuilder();
        for (char c : stk) {
            ans.append(c);
        }
        return ans.reverse().toString();
    }
}

C++

class Solution {
public:
    string removeDuplicateLetters(string s) {
        int n = s.size();
        int last[26] = {0};
        for (int i = 0; i < n; ++i) {
            last[s[i] - 'a'] = i;
        }
        string ans;
        int mask = 0;
        for (int i = 0; i < n; ++i) {
            char c = s[i];
            if ((mask >> (c - 'a')) & 1) {
                continue;
            }
            while (!ans.empty() && ans.back() > c && last[ans.back() - 'a'] > i) {
                mask ^= 1 << (ans.back() - 'a');
                ans.pop_back();
            }
            ans.push_back(c);
            mask |= 1 << (c - 'a');
        }
        return ans;
    }
};

Go

func removeDuplicateLetters(s string) string {
	last := make([]int, 26)
	for i, c := range s {
		last[c-'a'] = i
	}
	stk := []rune{}
	vis := make([]bool, 128)
	for i, c := range s {
		if vis[c] {
			continue
		}
		for len(stk) > 0 && stk[len(stk)-1] > c && last[stk[len(stk)-1]-'a'] > i {
			vis[stk[len(stk)-1]] = false
			stk = stk[:len(stk)-1]
		}
		stk = append(stk, c)
		vis[c] = true
	}
	return string(stk)
}

func removeDuplicateLetters(s string) string {
	count, in_stack, stack := make([]int, 128), make([]bool, 128), make([]rune, 0)
	for _, c := range s {
		count[c] += 1
	}

	for _, c := range s {
		count[c] -= 1
		if in_stack[c] {
			continue
		}
		for len(stack) > 0 && stack[len(stack)-1] > c && count[stack[len(stack)-1]] > 0 {
			peek := stack[len(stack)-1]
			stack = stack[0 : len(stack)-1]
			in_stack[peek] = false
		}
		stack = append(stack, c)
		in_stack[c] = true
	}
	return string(stack)
}

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