1326. Minimum Number of Taps to Open to Water a Garden

class Solution {
public:
    int minTaps(int n, vector<int>& ranges) {
        vector<int> dp(n + 1, 0x3f3f3f3f);
        dp[0] = 0;
        for(int i = 0; i < ranges.size(); ++i) {
            int l = max(0, i - ranges[i]);
            int r = min(n, i + ranges[i]);
            for(int j = l; j <= r; ++j) {
                dp[j] = min(dp[j], dp[l] + 1);
            }
        }
        int ans = 0;
        for(int i = 0; i <= n; ++i) {
            if(dp[i] == 0x3f3f3f3f) {
                return -1;
            }
            ans = max(ans, dp[i]);
        }
        return ans;
    }
};