763. 划分字母区间

Posted 2020-12-16 yonezu

 

方法一：滑动窗口

class Solution {
    public List<Integer> partitionLabels(String s) {
        List<Integer> res = new ArrayList<>();
        int[] arr = new int[128];
        for(char c : s.toCharArray()) {
            arr[c]++;
        }
        int[] window = new int[128];
        int n = s.length(), i = 0, j = 0, sumChar = 0, count = 0;
        while(j < n) {
            char c = s.charAt(j++);
            if(window[c] == 0) sumChar++;  
            if(++window[c] == arr[c]) count++;
            if(sumChar == count) {
                res.add(j - i);
                i = j;
                sumChar = 0;
                count = 0;
            }
        }
        return res;
    }
}

方法二：贪心，考虑好每个字符的最远出现位置

class Solution {

    public List<Integer> partitionLabels(String s) {
        List<Integer> res = new ArrayList<>();
        int[] arr = new int[26];  // 存储每个字符最后一个位置
        for(int i = 0; i < s.length(); i++) {
            arr[s.charAt(i)-‘a‘] = i;
        }
        int start = 0,  j = 0;
        for(int i = 0; i < s.length(); i++) {
            j = Math.max(j,arr[s.charAt(i)-‘a‘]);// j为当前遍历字符的最远的位置
            if(i == j) { // 当前包含所有已遍历字符就可以加入
                res.add(i - start + 1);
                start = i + 1;
            }
        }
        return res;
    }
}