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484. Find Permutation

484. Find Permutation

作者: Jeanz | 来源:发表于2018-01-12 10:33 被阅读0次

    By now, you are given a secret signature consisting of character 'D' and 'I'. 'D' represents a decreasing relationship between two numbers, 'I' represents an increasing relationship between two numbers. And our secret signature was constructed by a special integer array, which contains uniquely all the different number from 1 to n (n is the length of the secret signature plus 1). For example, the secret signature "DI" can be constructed by array [2,1,3] or [3,1,2], but won't be constructed by array [3,2,4] or [2,1,3,4], which are both illegal constructing special string that can't represent the "DI" secret signature.

    On the other hand, now your job is to find the lexicographically smallest permutation of [1, 2, ... n] could refer to the given secret signature in the input.

    Example 1:

    Input: "I"
    Output: [1,2]
    

    Explanation: [1,2] is the only legal initial spectial string can construct secret signature "I", where the number 1 and 2 construct an increasing relationship.

    Example 2:

    Input: "DI"
    Output: [2,1,3]
    

    Explanation: Both [2,1,3] and [3,1,2] can construct the secret signature "DI",
    but since we want to find the one with the smallest lexicographical permutation, you need to output [2,1,3]

    Note:

    • The input string will only contain the character 'D' and 'I'.
    • The length of input string is a positive integer and will not exceed 10,000

    一刷
    题解:
    For example, given IDIIDD we start with sorted sequence 1234567
    Then for each k continuous D starting at index i we need to reverse [i, i+k] portion of the sorted sequence.

    IDIIDD
    1234567 // sorted
    1324765 // answer

    public int[] findPermutation(String s) {
            int n = s.length(), arr[] = new int[n + 1]; 
            for (int i = 0; i <= n; i++) arr[i] = i + 1; // sorted
            for (int h = 0; h < n; h++) {
                if (s.charAt(h) == 'D') {
                    int l = h;
                    while (h < n && s.charAt(h) == 'D') h++;
                    reverse(arr, l, h); 
                }   
            }   
            return arr;
        }   
    
        void reverse(int[] arr, int l, int h) {
            while (l < h) {
                arr[l] ^= arr[h];
                arr[h] ^= arr[l];
                arr[l] ^= arr[h];
                l++; h--;
            }   
        }
    

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