README_EN.md

08.08. Permutation II

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Description

Write a method to compute all permutations of a string whose charac­ ters are not necessarily unique. The list of permutations should not have duplicates.

Example1:

 Input: S = "qqe"

 Output: ["eqq","qeq","qqe"]

Example2:

 Input: S = "ab"

 Output: ["ab", "ba"]

Note:

1. All characters are English letters.
2. 1 <= S.length <= 9

Solutions

Python3

Java

JavaScript

/**
 * @param {string} S
 * @return {string[]}
 */
var permutation = function (S) {
    let res = [];
    let arr = [...S];
    arr.sort();
    let prev = [];
    let record = new Array(S.length).fill(false);
    dfs(arr, 0, prev, record, res);
    return res;
};

function dfs(arr, depth, prev, record, res) {
    if (depth == arr.length) {
        res.push(prev.join(""));
        return;
    }
    for (let i = 0; i < arr.length; i++) {
        if (record[i]) {
            continue;
        }
        // 剪枝
        if (i > 0 && arr[i] == arr[i - 1] && record[i - 1]) {
            continue;
        }
        prev.push(arr[i]);
        record[i] = true;
        dfs(arr, depth + 1, prev, record, res);
        // 回溯
        prev.pop();
        record[i] = false;
    }
}

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