提交代码

class Solution {
    public int longestSubstring(String s, int k) {
    	if(s==null)	return 0;
        int res=0, curMax=0;
        
        for(int i=0;i<=s.length()-k;i++) {
        	curMax = checkSubstring(i,s, k);
        	res = curMax>res?curMax:res;
        	if(res>s.length()-i) 	break;
        }
        return res; 
    }
    
    private int checkSubstring(int start, String s, int k) {
    	int res=0;
    	int[] letters = new int[26];
    	Arrays.fill(letters, 0);
    	
    	for(int i=start;i<s.length();i++) {
    		letters[s.charAt(i)-'a'] ++;
    		if(letters[s.charAt(i)-'a']>=k) {
    			res=satiate(letters, k)?i-start+1:res;
    		}
    	}
    	
    	return res;
    }
    
    private boolean satiate(int[] nums, int minNum) {
    	for(int n: nums)
    		if(n!=0&&n<minNum)	return false;
    	return true;
    }
}

运行结果