LeetCode 821. Shortest Distance to a Character

题意：给定一个小写字符串以及一个在小写字符串中的字母，字符串长度为[1, 10000]。返回字符串中每个字母离给定字母的最短距离序列。

举例：

Input: S = "loveleetcode", C = 'e'
Output: [3, 2, 1, 0, 1, 0, 0, 1, 2, 2, 1, 0]

分析：对于每个字母，分别预处理它左边和右边离其最近的给定字母的下标，最后取最小值即可。

class Solution {
public:
    vector<int> shortestToChar(string S, char C) {
        const int MAXN = 10000 + 10;
        int left[MAXN], right[MAXN];
        memset(left, -1, sizeof left);
        memset(right, -1, sizeof right);
        int len = S.size();
        int tmp = -1;
        for(int i = 0; i < len; ++i){
            if(S[i] == C) tmp = i;
            left[i] = tmp;
        }
        tmp = -1;
        for(int i = len - 1; i >= 0; --i){
            if(S[i] == C) tmp = i;
            right[i] = tmp;
        }
        vector<int> ans;
        for(int i = 0; i < len; ++i){
            int tmpl, tmpr;
            if(left[i] != -1) tmpl = i - left[i];
            else tmpl = len;
            if(right[i] != -1) tmpr = right[i] - i;
            else tmpr = len;
            ans.push_back(min(tmpl, tmpr));
        }
        return ans;
    }
};