If after i steps, the maximum flipped position is i, then all positions 1..i have been flipped, so the prefix is aligned. We can track the max position after each step and count how many times max == i.

Approach

Initialize max_pos = 0, ans = 0.
For each step i (1-based), update max_pos = max(max_pos, flips[i-1]).
If max_pos == i, increment ans.
Return ans.

Code

[{"language":"C++","code":"class Solution {\npublic:\n    int numTimesAllBlue(vector<int>& flips) {\n        int ans = 0, max_pos = 0;\n        for (int i = 0; i < flips.size(); ++i) {\n            max_pos = max(max_pos, flips[i]);\n            if (max_pos == i+1) ans++;\n        }\n        return ans;\n    }\n};","lang":"cpp","html":"<pre class=\"shiki shiki-themes github-light github-dark\" style=\"background-color:#fff;--shiki-dark-bg:#24292e;color:#24292e;--shiki-dark:#e1e4e8\" tabindex=\"0\"><code><span class=\"line\"><span style=\"color:#D73A49;--shiki-dark:#F97583\">class</span><span style=\"color:#6F42C1;--shiki-dark:#B392F0\"> Solution</span><span style=\"color:#24292E;--shiki-dark:#E1E4E8\"> {</span></span>\n<span class=\"line\"><span style=\"color:#D73A49;--shiki-dark:#F97583\">public:</span></span>\n<span class=\"line\"><span style=\"color:#D73A49;--shiki-dark:#F97583\">    int</span><span style=\"color:#6F42C1;--shiki-dark:#B392F0\"> numTimesAllBlue</span><span style=\"color:#24292E;--shiki-dark:#E1E4E8\">(</span><span style=\"color:#6F42C1;--shiki-dark:#B392F0\">vector</span><span style=\"color:#24292E;--shiki-dark:#E1E4E8\">&#x3C;</span><span style=\"color:#D73A49;--shiki-dark:#F97583\">int</span><span style=\"color:#24292E;--shiki-dark:#E1E4E8\">></span><span style=\"color:#D73A49;--shiki-dark:#F97583\">&#x26;</span><span style=\"color:#E36209;--shiki-dark:#FFAB70\"> flips</span><span style=\"color:#24292E;--shiki-dark:#E1E4E8\">) {</span></span>\n<span class=\"line\"><span style=\"color:#D73A49;--shiki-dark:#F97583\">        int</span><span style=\"color:#24292E;--shiki-dark:#E1E4E8\"> ans </span><span style=\"color:#D73A49;--shiki-dark:#F97583\">=</span><span style=\"color:#005CC5;--shiki-dark:#79B8FF\"> 0</span><span style=\"color:#24292E;--shiki-dark:#E1E4E8\">, max_pos </span><span style=\"color:#D73A49;--shiki-dark:#F97583\">=</span><span style=\"color:#005CC5;--shiki-dark:#79B8FF\"> 0</span><span style=\"color:#24292E;--shiki-dark:#E1E4E8\">;</span></span>\n<span class=\"line\"><span style=\"color:#D73A49;--shiki-dark:#F97583\">        for</span><span style=\"color:#24292E;--shiki-dark:#E1E4E8\"> (</span><span style=\"color:#D73A49;--shiki-dark:#F97583\">int</span><span style=\"color:#24292E;--shiki-dark:#E1E4E8\"> i </span><span style=\"color:#D73A49;--shiki-dark:#F97583\">=</span><span style=\"color:#005CC5;--shiki-dark:#79B8FF\"> 0</span><span style=\"color:#24292E;--shiki-dark:#E1E4E8\">; i </span><span style=\"color:#D73A49;--shiki-dark:#F97583\">&#x3C;</span><span style=\"color:#24292E;--shiki-dark:#E1E4E8\"> flips.</span><span style=\"color:#6F42C1;--shiki-dark:#B392F0\">size</span><span style=\"color:#24292E;--shiki-dark:#E1E4E8\">(); </span><span style=\"color:#D73A49;--shiki-dark:#F97583\">++</span><span style=\"color:#24292E;--shiki-dark:#E1E4E8\">i) {</span></span>\n<span class=\"line\"><span style=\"color:#24292E;--shiki-dark:#E1E4E8\">            max_pos </span><span style=\"color:#D73A49;--shiki-dark:#F97583\">=</span><span style=\"color:#6F42C1;--shiki-dark:#B392F0\"> max</span><span style=\"color:#24292E;--shiki-dark:#E1E4E8\">(max_pos, flips[i]

Related Tags